Electrical #1: Updating electrical from fuses to 100 amp sub-panel

  • Advertise with us
Blog entry by Witdom posted 09-05-2017 01:17 AM 527 reads 0 times favorited 1 comment Add to Favorites Watch
no previous part Part 1 of Electrical series no next part

I am upgrading my shop electric to a 100 amp sub-panel that will have a main switch at the top (SE box). I have currently have 6 circuits, all 20 amps with the proper wiring of 12 gauge wires. The shop is a 600SF garage that will be 100% a shop, adding some 220 lines later for perhaps an updated Table Saw and Welder. The breakers in the main panel are 2-20 amp breakers, not paired, so I am at a loss here too…....So, a few questions.
Can anyone tell me why the lower 3 are bridged on the left? And is there any challenge that will come up that I should be made aware of? Thanks in advance.

1 comment so far

View Mike_D_S's profile


603 posts in 2853 days

#1 posted 09-05-2017 05:50 AM


First off, I’m not an electrician (though I have shocked the living cr$p out of myself a few times). So my advice is worth what you paid for it.

But looking at that box, it looks like both the red and black wires on the left side are your incoming feeds. My guess is you actually have 220 at the box and each wire is one phase. They are daisy chained to three fuses each to give you your six circuits in the same way the backplane would distribute the power in a breaker panel.

The red ones look funny because you only have one circuit connected while the top has three, but if you ignore the connected load circuits you see each feed is powering three of the fused circuits.

I’m drawing some broad conclusions based on one picture and a paragraph of text, but this wiring seems relatively straight forward to me. So if this isn’t familiar to you, I’d strongly recommend getting an electrician to do the subpanel install if you don’t already have one lined up.

There are other details related to whether the shop(garage) is attached to the main house and how you handle the neutrals and grounding planes. Getting some of this stuff wrong can lead to problems from minor to severe down the road.


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

Have your say...

You must be signed in to post the comments.

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