sub-panel in attached garage - 40 yr old main panel

Old 12-22-04, 04:15 PM
Visiting Guest
Posts: n/a
Question sub-panel in attached garage - 40 yr old main panel

Id like to install a subpanel in my attached garage to support my woodworking habit, but the install is complicated by where and how the panel was originally installed.

The main panel is a circa 1960 Zinsco with a split bus. The top 6 breaker slots are always hot; the bottom eight slots are behind dual 50 amp breakers. The panel has a single combination ground/neutral bar.

Id like to replace the full height breaker currently supplying my garage lights with a half height dual 60 amp breaker (on the always hot side of the panel bus) and use that as the feeder breaker to the sub-panel. Total wire length from the main to the sub-panel will be less than 30 ft.

If Im reading the charts correctly #6 as a cable or in conduit or #8 run as individual conductors is required at 60 amps. Im leaning toward #8 individual conductors because I can purchase solid wire at that gauge, which should (I think) work better with the lug screws on the breaker. If Im wrong and its allowable to go with stranded #6 straight to the Zinsco breaker lugs Id rather do that.

The main panel is installed in a walk in closet, and because of the way its framed, I cant get to any additional knockouts with conduit.

The sub-panel in the garage would have four circuits 1 @ 120V/15A for lights, 1 @ 120V/20A for hand tools, and 2 @ 240V/30A. One of the 240V circuits would be dedicated to a dust collection system to be added later, the other would be used alternately by a 3 horse bandsaw or a 3 horse jointer/planer.

Heres what I think I know about connecting the new sub-panel: Its an attached garage, so no new ground rod needed. Four conductors run 30ft from the main panel to the sub-panel. Both neutral and ground attached to the combined neutral/ground bar in the main panel but each attaches to its own bar in the sub-panel.

Heres what I know I dont know:
1. Given that the conductors would run behind sheetrock and through an attic, is it okay to run them without conduit?
2. Are the #8 conductors going to be adequate? If not, can #6 stranded be used with the breaker lugs?
3. If the ground and neutral bars in the sub-panel are both supposed to be detached, does that mean neither should connect to the sub-panel case?
Old 12-22-04, 05:24 PM
Join Date: Sep 2003
Location: Central New York State
Posts: 13,246
Upvotes: 0
Received 0 Upvotes on 0 Posts
My understanding is that a 60 amp breaker requires number 6 copper wire.

You can run 6/3 with ground or you can run individual conductors in conduit.

At the main panel the ground and neutral get connected to the same place. At the sub panel the ground and neutral remain separated. The ground gets connected to the box, but the neutral must not.
Old 12-22-04, 06:29 PM
Join Date: Sep 2000
Location: United States
Posts: 17,733
Upvotes: 0
Received 1 Upvote on 1 Post
You have a split-bus panel. They were phased out a long time ago for safety reasons. Furthermore, because they partition the available power, they aren't as flexible to connect a subpanel from. You might consider a new panel.

Increasing the number or size of breakers on the always-hot side is ill-advised, hazardous and probably illegal. The problem is that these breakers serve together as a main disconnect. Increasing the number of switches that comprise the main disconnect above six is illegal.

Furthermore, increasing the amp rating on the always-hot side risks overheating the service conductors, since these breakers protect those conductors. This is also illegal, and much more dangerous.

Installing a new panel in a clothes closet is also currently illegal because it constitutes a hazard.

I do not advise proceeding until you replace the main panel.
Old 12-22-04, 07:12 PM
ampz's Avatar
Join Date: Feb 2004
Location: Philadelphia
Posts: 513
Upvotes: 0
Received 0 Upvotes on 0 Posts
I agree with John in every point he made. I'd also like to metion that Zinsco like FPE are notorious for not tripping,I would have the service changed & while the contractor is on site he can install the new sub-panel.
Old 12-22-04, 07:44 PM
Visiting Guest
Posts: n/a
It may not be as bad as it sounds

John and ampz,

Id love to replace the panel! Unfortunately because of the layout of the house, moving the panel out of the closet to the nearest location it would be legal under the current code puts it outside on a different wall of the house, apparently requires relocating the drop from the pole, and would require serious rework of the existing wiring since little if any of it would be able to reach the panel in the new location. The two quotes I got for having that done both approached $4K. Both electricians suggested just leaving the panel alone and putting in a sub-panel.

Id still love to replace the panel since it's a split bus, 40 years old, and I've read posts on other boards about problems with Zinsco panels. Unless there is some loophole out there that would allow me to replace the panel with a new one in the same location, Im not going to spend $4K to have it moved.

When counting switches that make up the main disconnect, how are dual pole breakers with joined switches counted, as one or two? Currently on the always-hot side there are the following breakers installed:
1 full height @ 20A feeding garage lights
1 full height @ 30A feeding garage outlets
2 half height @15A unused, switched off and taped
2 half height @ 30A - 240V circuit for clothes dryer (unused)
2 full height @ 30A 240V circuit for HVAC

Before I ran the lights for the garage, the 20A breakers position was occupied by the dual 60A Id like to use as a feeder breaker. The circuit was dedicated to a welder and used 10/3 cable. I know welders have different requirements, but the thought of #10 wire attached to 60A breakers still gives me the willies.

It looks to me like all but the HVAC could be taped or replaced with the feeder breaker and space fillers (assuming I can find some) leaving me well below what the potential load used to be when the welder was wired in. It would also leave me with a switch count for the main disconnect of either 2 or 4 depending on how the joined breakers are counted.

I'd been planning on putting in a 60A sub-panel on the theory that the breakers used as the master disconnect in the new panel would trip even if the Zinsco breaker used as the feeder didn't trip right away. It seems to me that would add a little bit more safety to the system over where it's at today.
Old 12-22-04, 08:53 PM
hornetd's Avatar
Join Date: Aug 2001
Location: Maryland
Posts: 646
Upvotes: 0
Received 0 Upvotes on 0 Posts

Your present panel layout sounds like a mess. In the main lug always hot portion of the panel you should only have two pole full sized breakers. You must be able to shut off all power to the house with not more than six throws of the hand. That portion of the panel is not meant to hold any half height breakers at all. Only the breakers listed on the panels labeling or those recognized by an electrical testing laboratory as equivalent should be installed in your panel. If you check you will find that the label that bares the listing mark only lists double pole breakers for use in the always hot portion of the panel. All single pole breakers should be located in one of the sections that is controlled by one of your full sized double pole fifty ampere breakers.
Tom H
Old 12-22-04, 09:22 PM
Join Date: Jan 2002
Location: Chicago
Posts: 1,860
Upvotes: 0
Received 0 Upvotes on 0 Posts
General purpose outlets are not be fed by a breaker larger then 20A (I think ). You have a 30A outlet feeding garage outlets?

Before you do anything I would suggest you find out the gauge of the incoming service conductor. The problem with putting another breaker on the hot side of the split-bus panel is that you can overload the service conductor. The only thing protecting it are the unswitched breakers.

You have a tough problem here. Adding the subpanel is easy. Making it safe is not however. I would relocate the main panel if it would be me. Perhaps making it an outdoor panel on the same wall? I don't know if that's possible where you are.
Old 12-22-04, 09:40 PM
Join Date: Sep 2000
Location: United States
Posts: 17,733
Upvotes: 0
Received 1 Upvote on 1 Post
ToasterKing, best advice would be to start saving your pennies towards that $4K. If you found lead paint on the windows and asbestos falling from the ceiling, you'd do something about it. Your electrical situation is just as serious. Unless you've lived in this house for the last 40 years, the home inspector should have advised you of these hazards when you bought the house.

Protect your family before tending to your woodworking.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: