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I have a subpanel in a detached workshop which is supplied by two 50 amp circuits from my home's main panel.

enter image description here

My goal is to add a 240v receptacle to power an air compressor.

I have an existing 14-50R receptacle already installed but I noticed that it's wired directly from the feeder lugs and bypasses any breaker in the subpanel. Is this okay? Seems sketchy.

enter image description here

I have two breaker slots that I could use instead; currently those slots have 20 amp breakers but I don't use those circuits for anything and could abandon them. Would it make sense to replace those breakers with 30 amp breakers and connect a 14-30R receptacle?

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    @manassehkatz-Moving2Codidact Actually no. Unlike nearly every other panel design, Zinsco provides both legs to every space (the bus bars are straight parallel rails that run the full length, not interleaved fingers). The panel actually can provide 240V using a two-pole breaker in those two thin spaces on the right. Still needs to be replaced before it burns the place down though.
    – nobody
    Jan 11 at 22:50
  • @nobody not only that, but the breakers are obviously designed with flippable bus clips, so you can put either element on either pole. Jan 11 at 23:50
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Feed-through like that is legal in general (the wires are protected by the breaker in the main panel) - however those lugs are almost certainly not rated to hold down two wires, but rather only one. You need a second set of proper lugs for the feed-through. But also in this case (as NoSparksPlease pointed out) you’re in a detached outbuilding so feed-through is not legal without a local shutoff.

Other possible issues in that box:

  • Black wire possibly smaller than 4 AWG remarked to white/neutral. Neutrals smaller than 4 AWG must be a native neutral color (white or gray). Photo is too small to see the gauge markings on the feed wires.
  • Blue wire apparently on the neutral bar, again looking smaller than 4 AWG. Must be 4 AWG to be re-marked as neutral, and must actually be re-marked if it is a neutral.
  • White wires on the two left breakers. It's OK to use whites as hot for 240V circuits in /2 cable, but these are 120V circuits in conduit. They need to be proper hot colors.
  • Panel is Zinsco with known fatal issues that can burn your house down: busbar contact problems, known breaker problems. Should be replaced promptly. Not a big job since this is a small sub-panel. Get more spaces while you're at it.
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    Based on all the responses here, I'll look to do a panel swap. Wanted to respond to some of the possible issues though. First, feed wires are all 8 AWG and I see 2 hots (both black) and 1 neutral (blue). I'm guessing your comment means 4 AWG is code? The panel is a Zinsco. I recently had my main panel, also a Zinsco, replaced and I'm very happy to have had that done. I guess this one is next.
    – Todd O.
    Jan 11 at 17:15
  • @ToddO. No, it means that 4AWG is the smallest wire size that you're allowed to re-mark as white for neutral. Anything smaller than 4AWG must have either white or grey insulation as manufactured and cannot be re-marked. 8AWG can be OK for a 50A circuit, but only 90C rated SE cable, afaik. What you have there is THW, which carries a 75C rating in this application, I believe, and probably has to follow the 60C table for sub-100A residential circuits, and so I think is limited to serving a 40A circuit, so that's potentially another violation. I'm sure someone will find you a code reference.
    – J...
    Jan 11 at 17:46
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    @J... Re: 60°C for under 100A, There is some confusion about interpreting 110.14(C)(1)(a) where it says "...shall be used only for one of the following: (1) Conductors rated for 60°C." and I think they stop reading, but if thou then proceedeth to (3) it says "conductors with a higher temperature rating if the equipment is listed and identified for use with such conductors". If he replaces the Zinsco panel the new one will be listed for 75°C wire and terminations, and he said the service panel was changed already so will likely be good, but #8 in that Zinsco will be 60°C, 40A. Jan 12 at 3:09
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    @NoSparksPlease Ah, no I found the bit that was tripping me up, and it was 240.4(D) because, regardless of 110.14(C)(1)(a), you can't put 20A into 14AWG. The small conductor derating stops at 10AWG, though, not 8AWG, which is what I was originally thinking. Agreed it should be fine with a new panel.
    – J...
    Jan 12 at 17:31
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You have ONE 50A - 240V circuit feeding the shop.

It's protected by a single 50A (double-space this being North American split phase) breaker. It has two hots (through the breaker) and one neutral.

It's therefore fine for it to connect to a 50A receptacle, directly. Edit: comments correctly point out that as a detached building, you need a local disconnect. Other answers point out that this is apparently a known daangerous panel and should be replaced. So, replace it with a panel with a main breaker, and there's your local shutoff.

If you are loading it anywhere near 50A, you can't use much of anything else or you can expect the breaker to trip. On the other hand, if your compressor only needs 30, 25, 20 or 15A, you should not slap a 50A plug on it and "plug-er-in" as the breaker will not protect your compressor from faults correctly in that case.

50A will support a rather large arc without tripping, as I have seen when my oven's heating element blew.

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  • Thank you for the correction on my phrasing. That makes sense. The motor on my compressor says "Volts 115-208/230; Amps 24/12". So, I definitely don't need 50A.
    – Todd O.
    Jan 11 at 0:51
  • Its a common confusion, as the system isn't particularly obvious (or normal, globally.)
    – Ecnerwal
    Jan 11 at 0:52
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    I don't see how he can feed that receptacle directly and satisfy the disconnecting means required for a detached shop in 225.31. Jan 11 at 1:17
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Sorry to say this, but what a mess! For starters, that looks like a Zinsco panel, which are notorious for the breakers not tripping and other failures.

Second, is that really a feed thru panel, or is it supplied from the main panel with 2 wires per leg? It's not code legal to have parallel feed wires on anything but service entrance feeds in a residential installation. What is the gauge size on the feeds?

Lastly if supposedly a feed thru setup, why is there only one neutral?

Recommendation: If Zinsco, rip that thing out and replace it with Cutler Hammer or Square D QO panel.

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    It is a Zinsco panel so I'll look to replace it. Feed wires are all 8 AWG: 2 hots (black) and 1 neutral (blue). Pulling new feed wires will be a bigger problem than the panel swap. Feeds are in a 1 inch underground conduit that's about 15 yards from the house.
    – Todd O.
    Jan 11 at 17:19
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    @ToddO. For a 50A feed you should have two #8 hots, #8 white or grey neutral, and a #10 green or bare ground. For 1" conduit that is half the legal fill, replacing the wire shouldn't be hard. I'd be thinking pulling in #4's and a 90A breaker! Jan 12 at 3:36
  • How can a particular panel model be responsible for breakers not tripping? Aren't panels completely passive? (The action is in the breakers?) (I seriously don't know how, that's why I'm asking, it's not that I doubt you.)
    – davidbak
    Jan 12 at 5:10
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    @davidbak 2 things: Zinsco breakers were notorious for not tripping in overload conditions. It got to the point where if you had a zinsco panel you couldn't get insurance on your house or sell it before replacing it. The other thing is the connections to the main buss bar was so poor that the breakers would "weld" themselves making replacement impossible. Thanks for the respectful question/comment. Jan 12 at 8:23
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"I have an existing 14-50R...wired directly from the feeder lugs and bypasses any breaker in the subpanel. Is this okay?"

No.

NEC 225 which applies to Outside Branch Circuits says:

225.31 Disconnecting Means. Means shall be provided for disconnecting all ungrounded conductors that supply or pass through a building or structure.

The code follows with various detail, but you need switches to disconnect everything, the most versatile method while eliminating that fire hazard Zinsco panel is to install a panel with a main breaker.

Most everything else has issues too: White wires used as hots, #8 (smaller than #4) neutrals phased white instead of solid color, Zinsco panel, no space for a 240v breaker, no apparent wire feeding ground rods, multiple wires landed in single-wire lugs.

Check (or download) the Installation Instructions for the compressor, it may specify breaker and wire size that may not directly align with general Code provisions for a 12A installation, but the Instructions are part of the UL/CSA/ETL Listing and must be followed to comply with NEC 110.3.

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    When replacing the panel you can likely get away with an 8-space panel, but a 12 space (like an HOM1224M100PC) is often the same price and will give you better options later on. Jan 11 at 4:39
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    Gotta agree with you on all your comments/answers. Rip that zinsco panel out, get proper feeds to the new one. But don't go Homeline Square D, Go QO square D, much higher quality. Jan 11 at 5:20

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