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View Trout121180's profile

Electrical issue

by Trout121180
posted 02-14-2018 01:22 AM


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67 replies

67 replies so far

View MrUnix's profile

MrUnix

7503 posts in 2739 days


#1 posted 02-14-2018 01:27 AM

This may help:

Conduit Fill Table

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

View Knockonit's profile

Knockonit

613 posts in 742 days


#2 posted 02-14-2018 01:32 AM

you want to get an electrical company to do the work, problem with running a secondary service is the size of wire, the distance you are running and the size of conduit, it does heat up when pulling lots of power. 100 ft is quite a long run for some wire size, think of it as a long extention cord, so to speak, if you have experience small cords on over 25 ft plus runs, you can tell of the drop in power, and usually will pop a breaker,

My rule of thumb is to figure how much power i’d need if i used everything, then calculate a shade over half,
as you usually don’t use but a third of power at one time, unless you are a huge shop. Being bigger is always better, so if you have to run new secondary power, go big, and don’t look back, there may be some “gotta have, units which could add to load.
good luck
Rj in az

View Trout121180's profile

Trout121180

44 posts in 648 days


#3 posted 02-14-2018 01:37 AM

I saw the table but unfortunately it might as well be in Chinese. also i would never dream of doing this myself. I just want to make sure my electrician isn’t missing anything. Or taking the more expensive route. I mean I trust him but only as much as I would trust any contractor.

-- Luke “I thought I was wrong once, but I was mistaken.” “If you wait till the last minute it only takes a minute.”

View Trout121180's profile

Trout121180

44 posts in 648 days


#4 posted 02-14-2018 01:54 AM

Also being just a one man shop I am never running more than one piece of machinery at a time. All I really need is to be ale to have a 30amp breaker or two. At least for now. And according to him the only thing that is stopping me is the wire run to the garage is too small. So to be more specific my questions are

1. What size wire do I need to run from the main breaker to the sub panel to allow for a 30amp breaker.

2. Is 3/4” conduit big enough to fit that wire.

I understand my electrician will know this but as I stated above just trying to see if anyone can come up with a better idea than his. And by better I mean less expensive.

Maybe down the road I will break down and just pay for 100amp service out there. But for right now I am just hoping to be able to run the 5hp planer. I would love to just do both but i just don’t have the money.

-- Luke “I thought I was wrong once, but I was mistaken.” “If you wait till the last minute it only takes a minute.”

View Hermit's profile

Hermit

238 posts in 1865 days


#5 posted 02-14-2018 02:10 AM

Check with another electrician but I believe you can go 3 #8s and a #10 ground in 3/4 pipe. Which would allow you to go twin 50amp breakers. That way you could run more than just your 30 amp planer at a time. Otherwise 4-#10’s for 30 amp which is designed to trip at 24 amps. If you’re pulling wire, might as well go 3-#8s with #10 ground and plenty of soap. Secondly, how many bends/90’s do you have? More than 4 and you may have trouble pulling.

-- I'm like the farmer's duck. If it don't rain, I'll walk.

View Rayne's profile

Rayne

1243 posts in 2080 days


#6 posted 02-14-2018 02:20 AM



Check with another electrician but I believe you can go 3 #8s and a #10 ground in 3/4 pipe. Which would allow you to go twin 50amp breakers. That way you could run more than just your 30 amp planer at a time. Otherwise 4-#10 s for 30 amp which is designed to trip at 24 amps. If you re pulling wire, might as well go 3-#8s with #10 ground and plenty of soap. Secondly, how many bends/90 s do you have? More than 4 and you may have trouble pulling.

- Hermit

For a 100’ run underground, is that really sufficient? I looked around and it looks like he needs 3-#4’s and a #8 ground at the very least for a twin 60 amp breaker. I’m nowhere near an expert, but I’d be worried if it’s anything under that due to the run. The electrician will definitely be able to tell him. If going with #4’s, the 3/4” conduit is indeed too small.

View Richard's profile

Richard

11307 posts in 3573 days


#7 posted 02-14-2018 02:26 AM

Get a Licensed Electrician to do the work! INSURANCE!!!! If something goes wrong and they find out YOU did the wiring, You’re NOT COVERED!

-- Richard (Ontario, CANADA)

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Hermit

238 posts in 1865 days


#8 posted 02-14-2018 02:31 AM

I’m no expert but do know he can at least go to a 30 amp in 3/4 pipe. Again, contact another licensed electrician. It costs you nothing.

-- I'm like the farmer's duck. If it don't rain, I'll walk.

View Rayne's profile

Rayne

1243 posts in 2080 days


#9 posted 02-14-2018 02:32 AM



Get a Licensed Electrician to do the work! INSURANCE!!!! If something goes wrong and they find out YOU did the wiring, You re NOT COVERED!

- Rick

He’s not doing it. He just wants second opinions from us to see if his electrician is correct about the 3/4” conduit size being too small; you know, to help from being swindled. .

View Trout121180's profile

Trout121180

44 posts in 648 days


#10 posted 02-14-2018 02:36 AM

The only problem with checking with another electrician is trying to get one out in a reasonable amount of time with out him charging you an arm and a leg. I have used this guy before and have some what of a report with him. I guess I was looking for some miracle answer that doesn’t exist.

Hermit,
I am going to propose what you gave me to him. Thank you for spending the time to break things down for me.

I may just end up biting the bullet and burying new conduit. What a waste. I can’t believe the previous home owner wouldn’t spring for bigger conduit. What a waste. This really put a damper on things. Now it looks like holding off on a planer or not getting what I wanted to get. And since I really had my heart set on it I can’t imagine settling for something else.

-- Luke “I thought I was wrong once, but I was mistaken.” “If you wait till the last minute it only takes a minute.”

View Rayne's profile

Rayne

1243 posts in 2080 days


#11 posted 02-14-2018 02:45 AM



The only problem with checking with another electrician is trying to get one out in a reasonable amount of time with out him charging you an arm and a leg. I have used this guy before and have some what of a report with him. I guess I was looking for some miracle answer that doesn’t exist.

Hermit,
I am going to propose what you gave me to him. Thank you for spending the time to break things down for me.

I may just end up biting the bullet and burying new conduit. What a waste. I can’t believe the previous home owner wouldn’t spring for bigger conduit. What a waste. This really put a damper on things. Now it looks like holding off on a planer or not getting what I wanted to get. And since I really had my heart set on it I can’t imagine settling for something else.

- Trout121180

Maybe you could reduce the cost of the new conduit install if you rent a small excavator and dig the trench yourself. Maybe get the details from your electrician to see what you could do to reduce it. I can’t imagine it costing too much more for running the conduit if the ends are easy to access and reroute it to the new one. (well, that’s what I would do if I was in your position).

View JBrow's profile

JBrow

1368 posts in 1460 days


#12 posted 02-14-2018 02:56 AM

Trout121180,

It may be worth a phone call to your county/city electrical inspector. They should be able to tell you what upgrade can be achieved without replacing the ¾” conduit.

Since I am not an electrician, I could well be wrong, but is seems that #6 copper conductors can handle 50 amps up to a distance of 115 feet. From Mr. Unix’s table, it looks like # 6 may be allowed in ¾” pipe. But, as Hermit points out, pulling those conductors 100’ in ¾” pipe may be impractical.

Another option if trenching is required may be direct buried service entrance cable. However I am not knowledgeable of current code or rules in your area. If allowed, it may save some money. From what I recall, it requires no conduit and aluminum direct buried cable may be cheaper than copper conductors. However, the new trench may need to be deeper, adding to labor costs.

View WhyMe's profile

WhyMe

1182 posts in 2101 days


#13 posted 02-14-2018 03:11 AM

3/4” conduit can handle four #6 Cu THHN/THWN. Run three #6 and one #10. This can be fed by up to a 70A breaker. A 100ft is of no issue.

View msinc's profile

msinc

567 posts in 1044 days


#14 posted 02-14-2018 03:42 AM


Check with another electrician but I believe you can go 3 #8s and a #10 ground in 3/4 pipe. Which would allow you to go twin 50amp breakers. That way you could run more than just your 30 amp planer at a time. Otherwise 4-#10 s for 30 amp which is designed to trip at 24 amps. If you re pulling wire, might as well go 3-#8s with #10 ground and plenty of soap. Secondly, how many bends/90 s do you have? More than 4 and you may have trouble pulling.

- Hermit

For a 100 run underground, is that really sufficient? I looked around and it looks like he needs 3-#4 s and a #8 ground at the very least for a twin 60 amp breaker. I m nowhere near an expert, but I d be worried if it s anything under that due to the run. The electrician will definitely be able to tell him. If going with #4 s, the 3/4” conduit is indeed too small.

- Rayne

You are correct sir, it is not enough. For a 100 ft run he should have #4 wire {minimum} and he could use a 50 amp breaker for a main in the sub panel. Then he would have whatever various breakers less than 50 he needs. That voltage drop is what will get you…the very first thing to look at is how many volts he currently has in the main panel he intends to feed from. I just had separate 200 amp service ran to what is going to be my new shop. It was 125 feet away. You get to a point where the run is too long to simply sub feed. I get that nobody wants to spend the money for another service, but it really is the best way to go when you get a run that is over 50 feet or so.
Zero chance that 3/4 conduit is going to do much good.

View B4B's profile

B4B

163 posts in 1898 days


#15 posted 02-14-2018 03:47 AM

Without knowing your workflow, I’ll say this.

If you are upgrading your sub panel, go worth a 100amp service, at a minimum.

That’s either 1/0 aluminum, or #1 copper. That will keep voltage drop under 3% for the entire run (150 feet from panel to panel).

That most definitely means a larger conduit.

At this size, 1/0 aluminum is perfectly safe, most feeders for your utility drop to your panel are aluminum.

Option two is to stuff the existing conduit to it’s max fill. Just keep in mind if you add a dust collector to your shop, that’ll be at least two pieces of 240v equipment drawwing power at the same time.

-- There's two routers in my vocab, one that moves data and one that removes wood, the latter being more relevant on this forum.

View Trout121180's profile

Trout121180

44 posts in 648 days


#16 posted 02-14-2018 03:51 AM

It’s basically a straight shot from the house to the garage. I don’t believe there would be any bends. And I appreciate all the help guys I really do!!! I am just really surprised that this guy cheaped out with the conduit. Everything else that he had done in the house is done right!!! It just seems like common sense that if you are going to spend the money to run power out to the garage you would send more than 30amp service. He was a big car guy so you would think he would maybe might want to run a welder or car lift or something. Sorry. Just venting. I guess I should be happy that he had a 24’x24’ garage built when we already have an oversized two car garage attached to the house. I guess it’s all about perspective. I am talking with my electrician tomorrow. I will let you guys know what his plan is and what it’s going to cost me to see if I should try and get someone else out here for a quote.

-- Luke “I thought I was wrong once, but I was mistaken.” “If you wait till the last minute it only takes a minute.”

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woodbutcherbynight

5974 posts in 2949 days


#17 posted 02-14-2018 04:28 AM

Take in mind that conduit was not meant to be filled to capacity with wire. Cramming more wire into this smaller space creates heat issues which can cause fire. Granted we are talking worst case but that is how codes come into existence in the first place, disasters.

Now if you are going to run new wire to your shop and do not have water already consider at the least putting in a pipe and having it already in the ground (not in same trench) so if you choose later it is a much less expensive task. If I ever build a new shop I plan on a 1/2 bath with a shower because I do not always do woodworking and some task are that nasty that you don’t want it in the house. Electrical service, 100 amp service. Now to win the lottery to pay for all that.

LOL

-- Live to tell the stories, they sound better that way.

View chrisirving's profile

chrisirving

122 posts in 972 days


#18 posted 02-14-2018 10:34 AM

I’m an electrical contractor, I think one thing being overlooked is that it’s very often impossible to repull new wiring in an existing underground conduit. I’m sure the conduit and wiring were sized correctly for the existing load for a two car garage with no anticipation of any additional load, having said that, I always pull #6 thhn to any garage just in case anything is added in the future.
Sounds like you need a larger feed and need to abandon the old feeder. When this is done the building will need to be brought up to code also, GFCI receptacles, new grounding (since it’s a detached building) and dedicated circuits where needed

View Sparks500's profile

Sparks500

255 posts in 871 days


#19 posted 02-14-2018 01:25 PM

This is one where I would have suggested a 1½” poly be cable plowed in between buildings. Cable plow will do less damage to the yard, larger conduit will give you future options. Cost difference between pipe sizes is minimal, and poly never leaks or rots. JMO.

-- A good day is any day that you're alive....

View RobHannon's profile

RobHannon

321 posts in 1071 days


#20 posted 02-14-2018 02:11 PM

Full disclosure I am not an electrician, but I have done a moderate amount of electrical work including running a sub panel to my detached garage. 3/4” for a 100’ run was a big mistake and your electrician is right that it is not sufficient if you want to go bigger. My run is about 60’ and I went with 2” conduit for a 60amp subpanel. I wish I had gone with 100amp now, but it certainly works as is for my needs. Depending on what is in the path between the outbuilding and your main panel, cable plowing may be the best option. I had to trench under a driveway and that certainly added complexity and in retrospect I would have paid someone to do it just to save time and backache.

Local laws are different everywhere so if you aren’t up to speed with what is required in your case, pay a professional. I am not one who says that about many things, but running services (gas, electric, water) underground can get real expensive if a mistake is made.

View Holbs's profile

Holbs

2249 posts in 2570 days


#21 posted 02-14-2018 02:21 PM

Is a overhead run an option with today’s electrical codes?

-- The Carpenter Bee is derived from the Ancient Greek word wood-cutter "xylokopos/ξυλοκὀπος"

View Robert's profile

Robert

3557 posts in 2021 days


#22 posted 02-14-2018 02:41 PM

The electrician knows what he’s talking about. This is a simple job.

I suggest you pull the wire but leave the old conduit as a run for a future cable like coax or network.

-- Everything is a prototype thats why its one of a kind!!

View JCamp's profile

JCamp

1008 posts in 1091 days


#23 posted 02-14-2018 02:58 PM

Personally I would get a buddy with a tractor that had a plow and use it to dig a nice deep ditch and run direct bury wire. id also over size it a bit since it is a long run and you may eventually get more equipment. Where I am I don’t have to worry about codes like some folks in the cities. Even if you only do the digging and running of the wire it should really knock down the cost cause the electrician only has to do the hook up

-- Whatsoever thy hand findeth to do, do it with all thy might

View Richard's profile

Richard

11307 posts in 3573 days


#24 posted 02-14-2018 06:20 PM


I m an electrical contractor, I think one thing being overlooked is that it s very often impossible to repull new wiring in an existing underground conduit. I m sure the conduit and wiring were sized correctly for the existing load for a two car garage with no anticipation of any additional load, having said that, I always pull #6 thhn to any garage just in case anything is added in the future. Sounds like you need a larger feed and need to abandon the old feeder. When this is done the building will need to be brought up to code also, GFCI receptacles, new grounding (since it s a detached building) and dedicated circuits where needed
- chrisirving

This is an Electrician Talking! He’s Right! “When this is done the building will need to be brought up to code also,” UH OH! $$$$$$$$$$$!!!

Is a Clean/New Overhead Run Possible?

Rick

-- Richard (Ontario, CANADA)

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Trout121180

44 posts in 648 days


#25 posted 02-14-2018 06:53 PM

Luckily the building is only a couple of years old. I already had a licensed electrician do some work in the building. Everything is ground correctly and gfis are in place up to code. Now as far as if anything else has to be done once more power is added I have no clue which is why I am going to be paying someone. And yes Chris V. Unfortunately it looks like you are correct. The only option I really seem to have is to start from scratch. Looks like the planer will have to wait. Now the question is anyone have a clue what it’s going to cost me to have 100amp service put in. It’s no more than a 100ft run. Obviously there will be variables but just looking for a ball park. $1000. $5000. I’m sure my electrician will give me a quote I’m just being impatient and want to know if I should even waste his time. If we are talking thousands and thousands of dollars it might just not happen. At least not right now.

-- Luke “I thought I was wrong once, but I was mistaken.” “If you wait till the last minute it only takes a minute.”

View Knockonit's profile

Knockonit

613 posts in 742 days


#26 posted 02-14-2018 07:39 PM

I’d say around 2k plus, problem is wire and conduit will be over half that, panel is cheap, breakers are about 150 i think, been awhile since i bought a 100 amp breaker.

You can do the work, size the wire, drop the conduit, pull the wire, to panel location, and let electrician do the rest.
good luck, great learning curve.

View WhyMe's profile

WhyMe

1182 posts in 2101 days


#27 posted 02-14-2018 08:53 PM

I will repeat… 3/4” conduit can handle four #6 Cu THHN/THWN. Run three #6 and one #10. This can be fed by up to a 70A breaker. A 100ft is of no issue for voltage drop. Use plently of lube and use the old wires to pull in the new.

People who are saying #4 Cu THHN/THWN is needed for 50A at 100ft are incorrect. #6 THHN/THWN is rated at 65A @ 75degC and can be on the next standard size breaker which is 70A. At a full 240V 70A load the VD is less than 3%.

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WhyMe

1182 posts in 2101 days


#28 posted 02-14-2018 09:04 PM

Trout121180, have you done load calculations to know that you do need a full 100A feed? You may find going with 60A to 70A will work and it will save you a ton of money by using the existing conduit and just pulling the #6 THHN.

View Trout121180's profile

Trout121180

44 posts in 648 days


#29 posted 02-14-2018 09:38 PM

Why me,
I sent you a email. But to answer your question as of right now I have no need for 100amp service. In fact everything in my shop is powered just fine. My compressor, table saw, dust collection, modine heater, jointer, are hooked and with no issues what so ever. I have never even popped a breaker once. And to be honest after I upgrade my planer I don’t think there is anything in the near future as far as big machinery goes that will require anything more than the 20amp breakers I already have. That is why at least for now all I want to accomplish is to have one 30amp breaker that I can use. Someone recommended trying the planer in one of the 230v 20amp outlets I have now. He said there is a chance that it would work as long as I’m not running anything else. he runs a 5hp table saw off a 20amp breaker and has never had a problem. According to him just because it says 5hp doesn’t mean it’s really 5hp. But the problem is you have to run a dust collector with a planer. I am not much of a risk taker. And I don’t want to have a 600lb several thousand dollar paper weight in my garage. Hopefully my electrician or any electrician in my area will agree with you and I will be back in business. I greatly appreciate your advice. I will let you know what he says. And when and if I end up getting my planer going I will be more than happy to post some pictures.

-- Luke “I thought I was wrong once, but I was mistaken.” “If you wait till the last minute it only takes a minute.”

View msinc's profile

msinc

567 posts in 1044 days


#30 posted 02-14-2018 09:51 PM

You are getting some bad or mis-information here. One person has suggested you need “new grounding” because the building is detached. This is incorrect and it is not NEC code. Per feed from the power company {you have one meter on your house correct??} you must only have one earth ground, period, end of story. If you sub feed to another building from an existing source, as it sounds like you are doing, you must run the ground all the way back to the main panel so it uses the one single earth ground for the main feed. If you install a second earth ground {“new grounding since it’s a detached building”} you now have potential for difference in voltage and that is bad and very definitely not to NEC code at all.
Looks like to me someone calling himself an electrical contractor would know that. I am sure after reading this he will tell us he meant just the grounds in the receptacles….need to be “new”....yeah, Okay.
Now, if you run a whole new power supply {another hook up from the power company with another meter} then you need another earth ground because you have a separate source.
I am always amazed at the electrical advice given on this forum….sooner or later someone is going to get hurt…bad.

View WhyMe's profile

WhyMe

1182 posts in 2101 days


#31 posted 02-14-2018 10:23 PM


You are getting some bad or mis-information here. One person has suggested you need “new grounding” because the building is detached. This is incorrect and it is not NEC code. Per feed from the power company {you have one meter on your house correct??} you must only have one earth ground, period, end of story. If you sub feed to another building from an existing source, as it sounds like you are doing, you must run the ground all the way back to the main panel so it uses the one single earth ground for the main feed. If you install a second earth ground {“new grounding since it s a detached building”} you now have potential for difference in voltage and that is bad and very definitely not to NEC code at all.
Looks like to me someone calling himself an electrical contractor would know that. I am sure after reading this he will tell us he meant just the grounds in the receptacles….need to be “new”....yeah, Okay.
Now, if you run a whole new power supply {another hook up from the power company with another meter} then you need another earth ground because you have a separate source.
I am always amazed at the electrical advice given on this forum….sooner or later someone is going to get hurt…bad.

- msinc

If the detached structure is supplied by a feeder that is supplying multiple circuits, such as using a subpanel, a grounding electrode system is required at the detached structure (NEC 250.32). The grounding electrode system is for directing lighting strikes to earth. The equipment ground is run with the feeder current carrying conductors between building panels and its purpose is to clear fault current. The electrode ground to earth and the equipment ground serve two different purposes.

I need to add that the bonding of the neutral and ground is only done at the main first disconnect location. The neutral is isolated from ground at secondary/subpanels.

View Trout121180's profile

Trout121180

44 posts in 648 days


#32 posted 02-14-2018 11:06 PM

All I know is that everything was up to code when I purchased the house. The previous owner was Meticulous with his paper work and still had the paper from the building inspector for both the deck and the garage, permit and all. Also when I had the house inspected he looked at both electrical boxes and the paper work and assured me everything was in order. All I have done since then was add a little bit bigger sub panel along with some outlets. All work was done by a licensed electrician. I don’t know anything about electricity but I do know enough not to hire “Bob the handy man” to do any electrical work.” Anybody that touches my breaker box will be licensed period. Now just because he is licensed doesn’t mean he won’t try and get some extra bucks out of me which is why I am on this forum asking questions.

On a side note I haven’t read a single thread that had anything to do with electricity that didn’t have some spirited debate. I appreciate every and anyone that has taken the time out of their busy day to respond to my post. But any information given to me is just for a reference. As I said before only a licensed will be doing any work.

-- Luke “I thought I was wrong once, but I was mistaken.” “If you wait till the last minute it only takes a minute.”

View chrisirving's profile

chrisirving

122 posts in 972 days


#33 posted 02-14-2018 11:40 PM



You are getting some bad or mis-information here. One person has suggested you need “new grounding” because the building is detached. This is incorrect and it is not NEC code. Per feed from the power company {you have one meter on your house correct??} you must only have one earth ground, period, end of story. If you sub feed to another building from an existing source, as it sounds like you are doing, you must run the ground all the way back to the main panel so it uses the one single earth ground for the main feed. If you install a second earth ground {“new grounding since it s a detached building”} you now have potential for difference in voltage and that is bad and very definitely not to NEC code at all.
Looks like to me someone calling himself an electrical contractor would know that. I am sure after reading this he will tell us he meant just the grounds in the receptacles….need to be “new”....yeah, Okay.
Now, if you run a whole new power supply {another hook up from the power company with another meter} then you need another earth ground because you have a separate source.
I am always amazed at the electrical advice given on this forum….sooner or later someone is going to get hurt…bad.

- msinc


And this is why I hesitate to give any electrical advice here. I actually do this for a living and have to pass inspections

View Mike_D_S's profile

Mike_D_S

596 posts in 2755 days


#34 posted 02-15-2018 04:50 AM

msinc,

Can you clarify your response a bit? Though I’m not an electrician, it is my understanding that 250.32(b) required a separate ground rod at the detached structure in the situation the OP presents where he’ll be using a feeder to a sub panel.

You’re response reads as you don’t need the additional ground rod at the detached structure. But i’m not sure if you meant that you don’t need the grounding rod or if you were trying to say that you need the grounding rod as well as the ground line running back to the main panel primary grounding plane?

Thanks,
Mike

-- No honey, that's not new, I've had that forever......

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Mike_D_S

596 posts in 2755 days


#35 posted 02-15-2018 04:51 AM

I was typing away while the other guys were posting apparently.

-- No honey, that's not new, I've had that forever......

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TheFridge

10859 posts in 2026 days


#36 posted 02-15-2018 05:22 AM


I will repeat… 3/4” conduit can handle four #6 Cu THHN/THWN. Run three #6 and one #10. This can be fed by up to a 70A breaker. A 100ft is of no issue for voltage drop. Use plently of lube and use the old wires to pull in the new.

People who are saying #4 Cu THHN/THWN is needed for 50A at 100ft are incorrect. #6 THHN/THWN is rated at 65A @ 75degC and can be on the next standard size breaker which is 70A. At a full 240V 70A load the VD is less than 3%.

- WhyMe

Ditto. 18 yrs electrical here.

Use the old wire to pull the new in. Put in a new breaker. Done.

If it’s only a couple years old there shouldn’t be any problems if all the joints are sound. Even if there’s rocks and mud you can always swab it.

Sounds like a 300-500$ to me.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View msinc's profile

msinc

567 posts in 1044 days


#37 posted 02-15-2018 11:48 AM


msinc,

Can you clarify your response a bit? Though I m not an electrician, it is my understanding that 250.32(b) required a separate ground rod at the detached structure in the situation the OP presents where he ll be using a feeder to a sub panel.

You re response reads as you don t need the additional ground rod at the detached structure. But i m not sure if you meant that you don t need the grounding rod or if you were trying to say that you need the grounding rod as well as the ground line running back to the main panel primary grounding plane?

Thanks,
Mike

- MikeDS

This pretty much covers what I am saying…..250.32{B} is an exception code:

By changing the provisions of previous 250.32(B)(2) to an exception to 250.32(B), the NEC can continue to include requirements that would be applicable to existing buildings or structures grounded using the grounded conductor, while at the same time strengthening the requirement of 250.32(B) as the main rule prohibiting the use of the grounded conductor for grounding purposes for new installations. This change also helps reduce the number of designs that seemingly invite the possibilities of inappropriate neutral-to-ground connections that can and often do happen later, which is uncontrollable by any code rule.

As an example, while complying with previous 250.32(B)(2), there may not be a “continuous metallic path” between the two buildings or structures at the time of installation or the inspection by the authority having jurisdiction (AHJ). However, at a later date a phone line might be run between the two buildings or structures. How about a metal gas pipe? What about a low-voltage intercom system between the two buildings? However innocent these actions might be, they provide a “continuous metal path” between the two buildings that has the potential to introduce a parallel path for grounding that could result in a difference of voltage potential between these two paths.

It’s not that you don’t “need” the additional ground, it’s that you don’t want it. Having two earth grounds opens the possibility of a potential of difference in voltage. At best you will destroy electrical equipment in the buildings, at worst somebody is going to get hurt. Code exceptions make it “doable” or maybe a better way of saying it is “inspectable”, they do not by any means make it right or suggested.
Now, all this said, the NEC is just a code…they don’t inspect anything. The AHJ {authority having jurisdiction} sets the inspection criteria to whatever they want. It amazes me to see some of these changes in regards to what they will and will not allow. I build houses in Maryland and Virginia. Electrical wise, the county in Va. lets quite a bit go electrical wise, while Md. is way beyond NEC. Plumbing is the opposite, Va. is decades ahead of Maryland with septic systems.
Three number 6 and a number 10 wire pulled thru 100 foot of 3/4” conduit??? Yeah, that’s happenin’!!!!! He wont have to worry about passing any inspections cause he will never get that pulled thru.

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Mike_D_S

596 posts in 2755 days


#38 posted 02-15-2018 01:05 PM

music,

I always find these discussions interesting, so I’m still a little confused.

What you say seems to go directly against my understanding of the secondary grounding rod at the remote structure. Assuming the second panel is wired in with what I understand to be compliance with a neutral and grounding circuit from the main panel and the neutral is not bonded to ground in the second, then lack of the second grounding rod at the remote structure creates a risk of induced voltage on the ground circuit from say a lightning strike on the main structure?

In the wiring as described above (neutral and ground, separated at the remote panel), then having additional metallic connections (gas pipe or whatever) between buildings doesn’t create secondary return paths as the isolated neutral doesn’t allow that. The case where these would end up as returns would be if there already existed a fault putting return current on the grounding plane?

The point you are making about not using a grounding rod seems to only be an issue when the neutral is bonded to ground at both panels?

Thanks,
Mike

-- No honey, that's not new, I've had that forever......

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WhyMe

1182 posts in 2101 days


#39 posted 02-15-2018 05:07 PM



Three number 6 and a number 10 wire pulled thru 100 foot of 3/4” conduit??? Yeah, that s happenin !!!!! He wont have to worry about passing any inspections cause he will never get that pulled thru.

- msinc

That is just plain false. If the conduit is instatlled correctly pulling three #6 and one #10 thru 3/4” is not a problem at 100ft. I’ve done it a few times. My suggestion is to pull stranded wire and have a helper lubing and feeding as you pull.

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Trout121180

44 posts in 648 days


#40 posted 02-15-2018 05:18 PM

Well we are going to find out soon enough. Electrcian should be coming next week. I will definitely post what ends up happening.

-- Luke “I thought I was wrong once, but I was mistaken.” “If you wait till the last minute it only takes a minute.”

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Mike_D_S

596 posts in 2755 days


#41 posted 02-15-2018 05:19 PM

Without getting into the feasibility of the exact wire count, what’s the method for pulling multiple wires 100 ft through conduit? How do you actually go about it?

-- No honey, that's not new, I've had that forever......

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WhyMe

1182 posts in 2101 days


#42 posted 02-15-2018 07:34 PM

Here’s a good video. Main thing is to keep the pull head as small as possible and stagger the wires to keep from having a big knot of wire at the connection with the pull tape/rope. https://www.youtube.com/watch?v=sMA9ybAtpzo

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jonah

2090 posts in 3839 days


#43 posted 02-15-2018 08:17 PM

You also want to lubricate, lubricate, and lubricate. Especially for small, metal conduit like 3/4”. You really need two people. One to feed and lubricate, and one to pull.

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Mike_D_S

596 posts in 2755 days


#44 posted 02-15-2018 09:23 PM

If burying a new conduit, is there any real downside to going to larger conduit sizes?

One of the reasons I’m interested in this discussion is I need to run a subpanel in my attached garage and the construction of my house doesn’t permit running the feeder inside without significant sheetrock or siding work. So I was going to trench around the outside perimeter and enter through the garage wall.

I was thinking to run 1”, but other than cost, any reason not to go with 1 1/2” or bigger?

It would be really overkill for me I understand, but as a general concept, if 1” is good, then is 2” better?

Mike

-- No honey, that's not new, I've had that forever......

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Fresch

454 posts in 2461 days


#45 posted 02-15-2018 10:19 PM

2” is real big, just need the size for the amps you need MDS.
Trout you can try to pull on the wire now to see if it moves, turned off, 100’ pull not hard for an Electrician we do it all the time. I can see where people who don’t pull wire for money could find it hard if not impossible; if it’s free in the pipe it will pull.
Whyme , nice pic. looks like how my shop is wired. I used my fishtape and Kleins to pull in my feeder, showed wife how to square the wire and lube, then did it all after she got white polywater on here hands! Haha, it’s like a body fluid for you non electrical guys.

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msinc

567 posts in 1044 days


#46 posted 02-15-2018 10:51 PM



music,

I always find these discussions interesting, so I m still a little confused.

What you say seems to go directly against my understanding of the secondary grounding rod at the remote structure. Assuming the second panel is wired in with what I understand to be compliance with a neutral and grounding circuit from the main panel and the neutral is not bonded to ground in the second, then lack of the second grounding rod at the remote structure creates a risk of induced voltage on the ground circuit from say a lightning strike on the main structure?

In the wiring as described above (neutral and ground, separated at the remote panel), then having additional metallic connections (gas pipe or whatever) between buildings doesn t create secondary return paths as the isolated neutral doesn t allow that. The case where these would end up as returns would be if there already existed a fault putting return current on the grounding plane?

The point you are making about not using a grounding rod seems to only be an issue when the neutral is bonded to ground at both panels?

Thanks,
Mike

- MikeDS

I understand that this is confusing. Sorry for that. Your last sentence is correct. In a perfect world….there would be no panels except those that do not have a jumper between the neutral and earth grounds. This is something they just started doing in the last ten years or so. Prior to that all panels had the neutral and earth grounds connected. That is why the code is called a “code exception”. The confusing part is when you have guys from different parts of the country that are held accountable to two different AHJ’s. One may allow for this exception no problem. Where I live they very definitely do not. Based on what I have seen they may even allow two earth grounds even when the neutral and earth is connected simply because they lack a clear understanding of the problem or danger this may cause.
Suggest you google “voltage potential difference danger” and if you really want to read something interesting google “stray voltage danger”. Sorry for the confusion. It doesn’t take no where near the amount of electricity some people would think it takes to hurt you.

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Mainiac Matt

9353 posts in 2869 days


#47 posted 02-15-2018 11:47 PM

With a 100’ run, I think you’re going to be stuck digging it all up and larger cable in larger conduit to a new sub panel… might as well go double ought to a 100 panel at that point. It’s going to cost you ~ a grand for the electrician on top of digging it all up.

It sounds like you have a pretty nice setup and are getting by with the 30 amp. I think I’d punt the 5 HP dream and put that money somewhere else.

-- Matt -- I yam what I yam and that's all what I yam

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WhyMe

1182 posts in 2101 days


#48 posted 02-16-2018 12:15 AM


I will repeat… 3/4” conduit can handle four #6 Cu THHN/THWN. Run three #6 and one #10. This can be fed by up to a 70A breaker. A 100ft is of no issue for voltage drop. Use plently of lube and use the old wires to pull in the new.

People who are saying #4 Cu THHN/THWN is needed for 50A at 100ft are incorrect. #6 THHN/THWN is rated at 65A @ 75degC and can be on the next standard size breaker which is 70A. At a full 240V 70A load the VD is less than 3%.

- WhyMe

I need to clarify the use of #6 THHN with a #10 THHN ground. I said the #6 THHN can be protected up to 70A and it can, but paired with a #10 for a ground limits the circuit to 60A because of the #10 ground. To use the #6 for 70A will require the ground to be #8.

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WhyMe

1182 posts in 2101 days


#49 posted 02-16-2018 12:25 AM



With a 100 run, I think you re going to be stuck digging it all up and larger cable in larger conduit to a new sub panel… might as well go double ought to a 100 panel at that point. It s going to cost you ~ a grand for the electrician on top of digging it all up.

It sounds like you have a pretty nice setup and are getting by with the 30 amp. I think I d punt the 5 HP dream and put that money somewhere else.

- Mainiac Matt

Do you realize 2/0 Cu is rated to 175A? Why would you run 2/0 Cu to a 100A panel? #3 Cu or #1 Al is good for 100A. A 100ft feeder using 2/0 Cu will cost about $800 just for the wire.

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TheFridge

10859 posts in 2026 days


#50 posted 02-16-2018 02:55 AM

Anything bigger than 1-1/4” pipe is way overkill.

I doubt any pipe below ground on a residential job is rigid or imc. Overkill as well.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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