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Update: I was asking "What to put in 60A GFCI breakers in Subpanel?" Answer: maybe The main panel! That is, the main panel would be the subpanel of the 60A GFCI breaker. It's like the main panel and subpanel got swapped!

Detail. I was asking what to put in 60A GFCI breaker in subpanel in case I'd need to swap the 30A to the bath heaters and 60A to other loads. Here is an idea (Harper and others familiar with my setup).

My purely 240v main panel has this remaining loads (all are 30A breakers and all using AWG 10 even to the lights):

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What if I'd separate the main breaker and body in the main panel. Then the main breaker would connected to the subpanel. And the main body in main panel would become the subpanel of the 60A output of the original subpanel. Here:

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So it's like the subpanel and main panel become swapped. And the original main panel would now be the output of 60A of this original subpanel:

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I'd use 60A GFCI breaker number 5. This can totally eliminate all the wire nuts in the original panel above which is due to 3 circuits joined into one breaker. I'd put them in original breaker.

In essence. What to put in 60A GFCI breakers in Subpanel? The main panel (minus the main breaker which will be connected to the subpanel, but rest of main panel will be output of the 60A GFCI breaker).

This way, the entire house will be protected by GFCI. Not only that. Even the entire main panel chassis will be protected too (and it can be covered without fear of electrified chassis since it can trip the 5mA GFCI).

But big question. Can the 60A GFCI breaker have the following loads (the remaining original panel loads and the ones in GFCI breaker 5 to be transferred and added to the loads)?

  1. Aircon 2.4hp room 2 (9A) (number 1 to 5 is from remaining loads)
  2. Aircon 2.5hp sala (10A)
  3. Aircon 1.5hp room 3 (5A)
  4. Aircon 1hp room 1 (3A)
  5. Lights ground floor (1A), 2nd floor (0.5A), attic (0.5A)
  6. Room 2 outlets (3A) (from original subpanel no. 5 GFCI breaker)
  7. Kitchen outlets (0.5A) (from original subpanel no. 5 GFCI breaker)
  8. Attic outlets (2A) (from original subpanel no. 5 GFCI breaker)

total load is 35A that will use the 60A GFCI breaker output. Again each wiring is AWG 10 and each non GFCI breaker in original panel is 30A.

Will this work? This way the aircons are each in their original 30A breaker.

Brilliant idea or technically flawed? Lol.

original message yesterday:

Last year I bought 6 GFCI breakers. 2 pcs are 60A, 4 pcs are 30A. I initially bought the 60A at amazon because it is the cheapest. I wasn't thinking then about the wire and breaker matching then as I didn't know about it yet.

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These are my exact loads presently running. I turned off all the breakers because I just put the 100A main breaker.

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Bigger view.

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I'm presently using each 60A breaker for 6000W bath heater (I have 2 heaters, each connected separately to 60A breaker as shown in the actual breaker pics). I know 6000W/240v= 25A. Wire used for all are AWG 10. My question. Someone told me I must use 30A for the 25A heater. But even if you have a single TV say 1A, you still use 10A breaker in the house for that single load. So how come I can't use the 25A bath heater in the 60A ampere when it's the only load? I mean, the wiring to the 60A won't overload because the only load is the 25A bath heater and nothing else put on that 60A breaker. At least it should trip if there is a short in the heater. But the AWG 10 which has capacity of 30A to 35A won't melt at all because the only load is 25A heater. So why can't you use it on the 60A breaker? NEC may not allow it. But what is the logical and technical reasoning for it?

Also in case I'll swap the 30A for the heater. What would I put in the 60A GFCI breakers then, the TV or fridges? All the other 4 loads are just low enough that even when I combined many appliances in one breaker. It won't exceed 10A in the rest of the 4 30A GFCI breakers in above label pic.

Thank you.

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3 Answers 3

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The problem is the breaker needs to protect both the loads and the wires. There are (at least) 3 different ways your 25A heater could fail, requiring a breaker trip:

  • Short Circuit - That is easy. A short pulling hundreds of Amps (or whatever the service will supply) will trip a 60A breaker almost as fast as it would trip a 30A breaker. Good
  • Ground Fault - A ground fault will trip a GFCI breaker at very low current, no matter what the rating of the breaker is (30A vs. 60A). Good
  • Moderate overload - This is the real problem. If you have some sort of fault in the heater - perhaps a component starting to fail but not totally failing (because if it totally failed it would either fail open - safe - or fail closed - short circuit). BAD In this situation, you could have 40A or 50A flowing through and it would not trip the 60A breaker. But it would melt your wires and start a fire.
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  • Presently, my AWG 10 wires to the heaters from the breakers pass through outside the house in conduit. Can I just upgrade the wires then to match the breaker 60A? What size must I use? And this setup would be ok? a 25A heater connected to 60A breaker and wire sized for 60A?
    – Jtl
    Feb 4, 2019 at 3:21
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    That would solve the wire vs. breaker mismatch. But the device (heater in this case) vs. breaker size is still an issue. If the device were to have a partial failure resulting in a constant 40A running through it, the breaker would not trip, the upgraded wires would be fine, but your heater - and quite possibly surrounding furnishings - might catch on fire. Not a likely problem, but breakers are to protect against the unlikely problems.
    – manassehkatz-Moving 2 Codidact
    Feb 4, 2019 at 3:36
  • How about this. I'd put two of these 30A breakers after the 60A to power each 25A bath heaters. Or 30A rail din breakers after the 60A. I don't want anothe space consuming panel. imagizer.imageshack.com/v2/800x600q90/924/t1YX1Q.jpg
    – Jtl
    Feb 4, 2019 at 4:23
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Breakers protect wires more than loads

If we only built for circuits working the way they're supposed to, we wouldn't need any of this stuff.

The purpose of breakering 10AWG at 30A is to ensure that misconfiguration or malfunction doesn't pull, say, 55A over that wire and overheat it. As an aside, it also protects the house from whatever happens inside the equipment when it pulls 55A instead of 24A.

I would re-task the 60A breakers to feed other subpanels. They're a bit large to use for small appliance branch circuits.

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    Subpanels sound like a good solution to me. You get the proper per circuit protection while still getting the overall GFCI that was the goal of this project.
    – manassehkatz-Moving 2 Codidact
    Feb 4, 2019 at 3:37
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    the idea is that in the sub-sub-panel, you'll have $10 breakers protecting your 10-20 amp branch circuits. The GFCI will protect the works.
    – Harper - Reinstate Monica
    Feb 4, 2019 at 4:09
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    Past the GFCI any local brand of panel would do. The hard part is behind you.
    – Harper - Reinstate Monica
    Feb 4, 2019 at 5:59
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    Yes, now you understand my paranoia about having all service panels fully steel encased. Unfortunately there's not large AFCIs, , I have searched myself. Part of the issue is that AFCIs literally listen to the sound of the circuit, arc faults sound exactly like hooking up speakers with the power on. If the circuit beyond the AFCI is too complex, it muddies the sound.
    – Harper - Reinstate Monica
    Feb 4, 2019 at 17:47
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    @Jtl that proposal is excellent. Great way to do it, providing it's possible to mechanically peform the work in a quality way.
    – Harper - Reinstate Monica
    Feb 5, 2019 at 4:27
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Circuit breakers are designed to be the weakest link in the circuit. They have the ability to disconnect themselves in the event of a malfunction like a short circuit, ground fault or an overload. You do not want the wires (or your appliances) to be the weakest link in the system; they would overheat and melt, hidden inside a wall, potentially causing a fire. Additionally, appliances and devices you've outlined in your notes should not be powered with branch circuits rated any more than 15 Amps. Here in Canada residential lights, for example, are not to be powered by circuits rated at more than 15 Amps. And certain other loads, like refrigerators, are required to be supplied by their own dedicated branch circuit, sharing that load with nothing else.

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    The narrow wires used in your lights could not handle 30 Amps. These wires would melt long before the 30 Amp breaker ever tripped. The breakers wouldn't ever detect a problem until well after everything had melted together. Remember; you want the breakers to be THE weakest, narrowest part of the entire system or circuit.
    – Chris Taylor
    Feb 4, 2019 at 3:38
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    You are using oversized breakers (30 amps) and oversized conductors (awg #10), which is fine, but don't forget the rest of the system like the plugs; they are only designed for maybe 20 amps, maximum. And what about those appliances you plug into your circuits? The wiring inside these appliances are inly thick enou to handle 15 or 20 amps at the most. The wiring inside these appliances would therefore be the weakest link in the electrical system and they could melt and be destroyed.
    – Chris Taylor
    Feb 4, 2019 at 3:45
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    You must use the smallest size breakers possible in every case, not the largest size. This is the basic principle behind every electrical circuit everywhere. Using larger ampacity breakers will eventually burn your house down. A short circuit in an 18 gauge wire may or may not trip a large 30 amp breaker.
    – Chris Taylor
    Feb 4, 2019 at 11:44
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    I dont know what you mean by "CR heater" and "CR outlets". Your breaker's ampacities should be based on the rating of the appliances you are using. In Canada we generally use no more than 12 devices on each general 15 amp circuit (plugs, lights, and so on) assuming each dvice is requires about 1amp. That means the demand is only ever about 80% of what each breaker can provide. Any more than 12 amps on a 15 amp circuit and you're close to getting nuisance tripping. Throw away those four 40 amp breakers and replace them with 15's. And replace those two 60's with two 30's.
    – Chris Taylor
    Feb 4, 2019 at 12:02
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    We call them 'bathrooms', 'restrooms' or simply 'washrooms'. We all have our own euphamisms, I suppose. Never ever install breakers unless you have done at least some kind of basic load calculations for each branch circuit. You'll probably require about eight 15 amp single-pole breakers for your general circuits. And I wouldn't use more than 25 or 30 amp breakers for the dedicated heater circuits.
    – Chris Taylor
    Feb 4, 2019 at 12:38

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