LumberJocks

Shed electrical questions.

  • Advertise with us

« back to Focus on the Workspace forum

Forum topic by Derrick posted 02-27-2020 07:10 PM 596 views 0 times favorited 43 replies Add to Favorites Watch
View Derrick's profile

Derrick

134 posts in 1812 days


02-27-2020 07:10 PM

Hello,

I’m currently building a detached shed, so we can clean up our garage to use as a small workspace.

The other goal of the shed is to install dust collection and an air compressor.

I’ve been reading the portion of the NEC that covers MWBC’s(210.4), and trying to make sense of it all.

Basically, I need 2×20a circuits. Since I can’t run two separate circuits into the shed, I’ll need to utilize a Multi Wire Branch Circuit.

I think I’ve got things figured out, but I just want to run things by some more knowledgeable resources.

Here’s my breaker box:

The cable run will need to come out the back of the box. I was thinking that unused mounting hole in the bottom left pic. Similar to the one on the lower right that was used when our AC was installed.

My shed is just behind the breaker box on a small slab we had poured last year. The cable run will be very short. Less than 15 feet away from the breaker box.

I’ve been trying to read as much as possible on MWBC’s. I’m comfortable around electricity. I plan on doing the job myself, and saving roughly $3k.

I want to pull all the permits and do everything correctly, I’m just trying to get my ducks in a row first.

Here’s a sketch I found that looks like exactly what I want to do:

For those who are familiar with powering their own shop, does this look correct for what I’m looking to do?

I know I need to free up some space in the box. I’ve been looking at the use of tandem breakers to do so.

Any help would be awesome!


43 replies so far

View clagwell's profile

clagwell

142 posts in 467 days


#1 posted 02-27-2020 07:26 PM

Yes but—- depending on the version of the code your local jurisdiction is using that breaker will probably need to be a GFI type (detached building). A 2 pole GFI breaker with neutral (for the MWBC) is not cheap. You might be better off making the shed a subpanel. It’s then treated as a service entrance and needs an additional ground rod. You can use a standard 2 pole breaker in your main panel and a cheap 100A main panel in your shed. Use a larger gauge for the feeder and get a lot more capability in the shed for not much extra cost.

-- Dave, Tippecanoe County, IN

View Derrick's profile

Derrick

134 posts in 1812 days


#2 posted 02-27-2020 07:54 PM



Yes but—- depending on the version of the code your local jurisdiction is using that breaker will probably need to be a GFI type (detached building). A 2 pole GFI breaker with neutral (for the MWBC) is not cheap. You might be better off making the shed a subpanel. It s then treated as a service entrance and needs an additional ground rod. You can use a standard 2 pole breaker in your main panel and a cheap 100A main panel in your shed. Use a larger gauge for the feeder and get a lot more capability in the shed for not much extra cost.

- clagwell

Ok. Finding out the version of the code that is used in my area should be done first. That makes sense.

I’ll get on that.

Thank you!

View tvrgeek's profile (online now)

tvrgeek

578 posts in 2323 days


#3 posted 02-27-2020 08:12 PM

First of all, what is the load? Both my dust collector and compressor are on 20A 220 circuits. Both are 1 3/4 HP. Then you are going to want a light at least, so a 110 circuit and probably a plug. Sounds like you should run a 40A branch to a sub panel. 2 220 breakers and a 110.

NEC is fine, but seems every jurisdiction makes amendments to it. For instance, here we need two ground rods 6 feet apart. Your county WEB should have it posted.

Twin half size breakers are a life-saver. You don’t want to know what it costs putting in a bigger panel!

View WhyMe's profile

WhyMe

1249 posts in 2235 days


#4 posted 02-27-2020 08:14 PM

As long as the feeder is buried to the proper depth you can use a regular 2 pole breaker or two singles tied together. You will need GFCI protection on the circuits in the shed and that can be done by using GFCI outlets as the first outlet in the circuit.

View Derrick's profile

Derrick

134 posts in 1812 days


#5 posted 02-27-2020 08:35 PM

My compressor is 15a and the DC is 20a 120v.

Yeah. The tandem breakers seem to be the solution to my space problems. I’m just trying to learn more about my breaker box and where or if they’re allowed. Just on quick searches, it seems that I can’t just install them wherever I want. I need locate where they’ll fit.

View controlfreak's profile

controlfreak

563 posts in 275 days


#6 posted 02-27-2020 08:47 PM

I ran a wire off a 100 AMP breaker to a 100 AMP sub Panel in the shed. I ran outlets every 6’ using two 20 AMP circuits. I put two outlets in each box using almond for one circuit and white for the other. One lighting circuit. One 220V heater and have some room for other items. If you use a GFCI as your first outlet the other outlets will also be protected. Hopefully you won’t need arc fault breakers, those trip out if you look at them wrong.

Permits, we don’t need no stinking permits! I am lucky, in my city the don’t really give DIY work a hard time and I know all the inspectors anyway. I do follow code for safety and to not get flagged by the home inspector when it is time to sell.

View Derrick's profile

Derrick

134 posts in 1812 days


#7 posted 02-27-2020 09:40 PM

The shed is a small 4×10. We live in the city, and don’t have a ton of room. Actually, where the shed is, I have to get a written agreement from my neighbor, because of it proximity to our lot line. No big deal there. Im only looking for a couple outlets for the dc and air compressor. Then I can run some cheapy LED shop lights from amazon or Costco. Nothing crazy.

I’m sure I could get by without pulling the permits or getting the final inspection, but those items are a small drop in the bucket compared to the price that I’ve been given by local electricians for the whole job. Plus for a potential DIY project, it gives me piece of mind.

View ibewjon's profile

ibewjon

1370 posts in 3467 days


#8 posted 02-27-2020 09:52 PM

Dave is correct, add a panel. NoAbout ground rods:. NEC requires 8’ in contact with soil, so an 8’ rod must be flush or buried, and requires the use of a direct burial rated ground clamp. And the code also requires 2 ground rods, properly spaced for your area, or a ground rod test to prove ground resistance. Two rods are cheaper than a test. 10’ ground rods can be left above grade for the connection. To handle tie two single pole breakers, a UL listed handle tie for breaker brand must be used, no wire or nail. Just buy the proper 2- pole breaker. Even with the ground rods at the shed, you still need the equipment ground from the main panel.

View Derrick's profile

Derrick

134 posts in 1812 days


#9 posted 02-27-2020 09:58 PM

A panel just for those 2 items? Isn’t that excessive?

View tvrgeek's profile (online now)

tvrgeek

578 posts in 2323 days


#10 posted 02-27-2020 10:02 PM

LED lights: HF has the great deal $30 5000 Lumen on sale for $20 if you get the coupons.

Sounds like you could rewire your tools for 220 if possible.

Some don’t consider it, but when I sold my house in MD, the inspector did look up the permits and fortunately, they found the one for the panels. They don’t get too upset about branch work, but a panel had better have a signature. O thought I was covered in the house I then bought, as the barn had a permit, but when I went to pull the electrical, I found out he had never had an occupancy, so I had to research the history, find the engineering drawings in the county archives, reapply and pay anwe for the original permit, then pull my electrical.

View ibewjon's profile

ibewjon

1370 posts in 3467 days


#11 posted 02-28-2020 12:15 AM

Not excessive at all. A 2- pole ( 240 v ) 60 a gfi breaker costs around $150. A 12 circuit panel and standard breakers and gfi receptacles are much less expensive. And if a single part fails, it will cost less to replace than the 60 amp gfi breaker.

View Derrick's profile

Derrick

134 posts in 1812 days


#12 posted 02-28-2020 12:24 AM



Not excessive at all. A 2- pole ( 240 v ) 60 a gfi breaker costs around $150. A 12 circuit panel and standard breakers and gfi receptacles are much less expensive. And if a single part fails, it will cost less to replace than the 60 amp gfi breaker.

- ibewjon

Oh no. Not price wise. Sorry. I know it’s nothing compared to what I would spend if I had someone else do it. I’m talking about effort wise. If that’s to code what I would need, I’m fine with that. The search I’ve turned up so far have mentioned doing the job either way. Sub panel/ground rods/etc vs. MWBC. The shed will never be more than it is. Just those to little 20a circuits, running those 2 pieces equipment.

Again. If that’s what I need per code, I’ll go with it, but if a multi wire branch will suffice, I’d rather go that direction.

View Derrick's profile

Derrick

134 posts in 1812 days


#13 posted 02-28-2020 04:17 AM

Ok, so it looks like Seattle uses the 2017 version of the NEC. Here’s what I can find for that:

Multiwire branch circuits
A multiwire branch circuit basically consists of two or more ungrounded conductors that share a neutral. All conductors of a multiwire branch circuit must originate from the same panelboard [210.4(A)].
For personnel safety, each multiwire branch circuit must have a means to simultaneously disconnect all ungrounded conductors at its origin [210.4(B)]. If that origin is two or more breakers, you can provide this disconnect by using single-pole circuit breakers with handle ties identified for the purpose [240.15(B)(1)].
Multiwire branch circuits can supply only line-to-neutral loads [210.4©], except that a multiwire branch circuit can also supply:
  • An individual piece of line-to-line utilization equipment, such as a range or dryer [210.4© Ex 1].
  • Both line-to-line and line-to-neutral loads if the circuit is protected by a device such as a multipole circuit breaker with a common internal trip that opens all ungrounded conductors of the multiwire branch circuit simultaneously under a fault condition [210.4© Ex 2].
    In multiwire branch circuits, the continuity of the neutral conductor must not be interrupted by the removal of a wiring device. In these applications, the neutral conductors must be spliced together at every device providing a pigtail to terminate to the wiring device [300.13(B)]. The opening of the ungrounded conductors, or the neutral conductor of a 2-wire circuit during the replacement of a device, doesn’t cause a safety hazard, so pigtailing these conductors isn’t required [110.14(B)]. Caution: If the continuity of the neutral conductor of a multiwire circuit is interrupted (opened), the resultant over- or undervoltage can cause a fire and/or destruction of electrical equipment.
    The ungrounded and neutral conductors of a multiwire branch circuit must be grouped together using cable ties or similar means at the point of origination [210.4(D)]. These conductors are not required to be grouped if they are contained in a single raceway or cable unique to that circuit, making the grouping obvious.
    If the ungrounded conductors of a multiwire circuit don’t terminate to different phases or lines, the currents on the neutral conductor will add instead of canceling each other out, possibly overloading the neutral conductor.
    Identification
    Equipment grounding conductors are allowed to be bare, covered, or insulated. Insulated equipment grounding conductors size 6 AWG and smaller must have a continuous outer finish — either green or green with one or more yellow stripe(s) [250.119]. If installing equipment grounding conductors
    4 AWG and larger, you can permanently reidentify the insulation with green markings or tape, or strip the insulation off of the conductor. This reidentification must be done at every point where the conductor is accessible [250.119(A)].
    Identify the neutral (“grounded”) conductor per 200.6. If 6 AWG or smaller, it must be white, gray, or some color other than green with white stripes along its entire length. For 4 AWG and larger, the same means of identification can be used, or it is allowed to use white or gray tape at terminations.

All pretty straight forward with the exception of the grouping. I’m still trying to figure that all out.

As far as the grounding goes, I think 250.32c covers that:

250.32 Buildings or Structures Supplied by a Feeder(s)
or Branch Circuit(s). (A) Grounding Electrode. Building(s) or structure(s) supplied by feeder(s) or branch circuit(s) shall have a grounding electrode or grounding electrode system installed in accordance with Part III of Article 250. The grounding electrode conductor(s) shall be connected in accordance with 250.32(B) or©. Where there is no existing grounding electrode, the grounding electrode(s) required in 250.50 shall be installed. Exception: A grounding electrode shall not be required where only a single branch circuit, including a multiwire branch circuit, supplies the building or structure and the branch circuit includes an equipment grounding conductor for grounding the normally non–current-carrying metal parts of equipment.

The issue with that info, is that I don’t know if it’s from 2017 or not. I pulled it from another forum.

Regardless, it does appear that my original sketch would work. Am I wrong thinking that way?

View clagwell's profile

clagwell

142 posts in 467 days


#14 posted 02-28-2020 11:41 AM

Your original sketch is fine except you will probably need a MWBC capable GFI in your panel, not just a simple 2 pole breaker.

-- Dave, Tippecanoe County, IN

View Derrick's profile

Derrick

134 posts in 1812 days


#15 posted 02-28-2020 12:12 PM


Your original sketch is fine except you will probably need a MWBC capable GFI in your panel, not just a simple 2 pole breaker.

- clagwell

This what I’m seeing so far:

For personnel safety, each multiwire branch circuit must have a means to simultaneously disconnect all ungrounded conductors at its origin [210.4(B)]. If that origin is two or more breakers, you can provide this disconnect by using single-pole circuit breakers with handle ties identified for the purpose [240.15(B)(1)].

As long as the two pole breaker is tied, it makes sense to me that as long as the outlets are both GFCI, it would suffice for proper disconnect. If one of the GFCI outlets pops, it’ll knock out both breakers. Whyme mentioned that above.

showing 1 through 15 of 43 replies

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com