50amp panel, can I feed a 30A/240 water heater?

1738 Views 16 Replies 8 Participants Last post by joe-nwt, Nov 16, 2020

teachermanalex

Discussion Starter · May 3, 2020 (Edited)

3

Hi Community,

My old house was re-wired about 20 years ago, and they put on a panel with 2 50-amp breakers in 2 phases (so 100 amps total).
I want to add a new heat-pump water heater, but that calls for a 240v 30Amp circuit -- so that's most of the capacity of the mains on this panel.

My question: Can I put in a new 240V/30A 2-pole breaker and add the water heater? Or am I inviting a whole lot of trouble?

I could upgrade the panel, but that would mean running a new underground feeder to it, which would start to get expensive.

The good news is, the house doesn't draw much power -- it's old so no A/C, no large appliances, etc. The biggest load in there is the 120v space heater.

Thanks!

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chandler48

· #2 · May 3, 2020

If the two 50 amp breakers are over and under each other and have handle ties, you only have 50 amps of service. Can you post a picture of your panel so we can see what you see? Your 120 v space heater will eat up a 20 amp circuit totally, so it is a hog for sure.

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seharper

· #3 · May 3, 2020

We're going to have a whole bunch of other questions about what the other loads in the house are. A photo of the panel may be helpful; you should be able to post photos on your second post.

Since a 50A service is *very unusual*, are you **sure** this is the only service panel in the entire house? Search very thoroughly, including outside. 20 years ago I would expect maybe a 50A subpanel off a 100A main panel.

Does this building have more than one occupancy (i.e. a duplex, apartment, anything like that)? Do you pay for your power or do you share the meter with anyone else?

Further, can you look closely at the wires coming into this panel? If they are 6 AWG we may be able to bump this panel to a 60.

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surferdude2

· #4 · May 3, 2020

If your panel has a 100 amp service feed, you can run the water heater quite well. Look for the main disconnect to see what size it is in amps. I suspect it's 100 amp but verify.

Rewiring a house to a 50 amp service would have been very odd.

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teachermanalex

Discussion Starter · #5 · May 3, 2020

2

Thanks, all. Answers to the questions:
Yes, this is unusual. Here is the setup:
- The house is a 2nd building on a 2-building parcel.
- The panel is essentially a sub-panel, fed from the meter/main at the street.
- This unit has a dedicated meter, but it is pretty far from the house panel. The house panel is the only load on the main panel at the meter.
- There is a ~100-foot run of 6AWG copper stranded feeder, buried between the two panel.
- This is definitely the only panel at the house.
- I assume they put 50A breakers at the panel rather than 60 because of the length of the run between the two panels.

Here are photos:

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surferdude2

· #6 · May 3, 2020

Looks like you'll be running pretty tight by adding a water heater. The room heater you use needs about 13 amps and the WH will need about 24 so... 37 amps on the high leg. That doesn't leave much for a refrigerator, TV, toaster, coffee pot, etc. It might work if you watch your step as to how you run the electives. Not ideal but should get by.

teachermanalex

Discussion Starter · #7 · May 3, 2020

Thanks, I posted photos & answers to your q's in the main thread.

surferdude2

· #8 · May 3, 2020 (Edited)

I'm wondering where the heat pump gets its power?? I also think you can safely upsize the main breaker to a 60... even a 70 will still be code compliant. That would give you more availability to operate normally.

RAL238

· #9 · May 3, 2020

The heat pump water heater might not be as bad of a load as you might think. I keep mine set to high efficiency mode, where it only heats water using the heat pump. The compressor draws under 4A when running. If I switch it over to hybrid mode, the heating elements will draw 19A, so it does require a 30A circuit.

seharper

· #10 · May 3, 2020

Let's see. First, I can't believe it! The panel is set up correctly -- oh wait.

- The Siemens-Murray MP-T breaker at the lower right doesn't fit the bus stabs properly in this Eaton panel. That needs to be an Eaton BR115. ($5).

- The two lower right breakers are a multi-wire branch circuit (they share a neutral). They are correct so far, but they need to be handle-tied with an Eaton BRHT or BRTCS. $4 at Home Depot.

- The two lower left breakers are also a multi-wire branch circuit. They need to either be handle-tied as above, or replaced with a 2-pole breaker Eaton BR220 ($10).

- I don't know why the lower right breaker is 15A. Maybe there is 14 AWG wire on this half of the circuit; that would be weird, but legal. If it's all 12 AWG, then either spend $9 on handle tie + Eaton BR120, or just spend $10 on an Eaton BR220.

Well, nobody's perfect. This one's pretty good. The alien breaker is the only red alert.

Apparently they downrated the breaker because of the "long distance" (100'). That isn't long enough to justify a downrate/wire size bump. That doesn't even begin to become a concern until about 165', not even in Canada. If it had been a 120V circuit, then Canadians start caring at about 80 feet, but it's not and you're not. (right?) So you are free to run the wire at full ampacity. If it is UF cable, your max amperage is 55A, but you are allowed to round up to the next available breaker, so 60A.

I think I see a little writing on 2 of the wires, but the way they're oriented, you can't see any writing anywhere else. Look closely for that. If there is writing, and it says THHN/THWN or XHHW wire, then you are allowed 65A. Again you can round up to 70A.

So with a wave of the NEC codebook, we have magically created 20A more power than you thought you had. Your heater needs 23A, et voilà! The power of following Code.

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surferdude2

· #11 · May 3, 2020 (Edited)

Taking a closer look... you'll see that the top and bottom breakers on the right side are a multi wire circuit and will require moving them so they are together and able to accommodate a handle tie. (providing you're required to bring it up to current code or just want to do it because it's a good idea)

Swap the second breaker with the bottom one and you'll be all set to tie the handles on both of the multiwire circuits on the right side. In the process, get the proper breaker for the 15 amp one.

teachermanalex

Discussion Starter · #12 · Nov 15, 2020

I want to say thank you to everyone who responded. Such great info.
I found a water heater that runs on 220V, 20-amps and installed it on the existing panel without upgrading the mains. So far so good -- although we haven't seen a winter yet so I may need to upgrade the mains breaker this month.

Thank you, thank you, esp. @seharper and @surferdude2

surferdude2

· #13 · Nov 15, 2020

@teachermanalex, Thank you for the update and the kind words. It sound like you're all set.

Best regards,
SD2

Jim Port

· #14 · Nov 16, 2020

Why do some continue to bring up code changes that changed after the installation and are still compliant if untouched? Is it to confuse or something else?

Blockisle9

· #15 · Nov 16, 2020

I agree with you

surferdude2

· #16 · Nov 16, 2020

Jim Port said:
Why do some continue to bring up code changes that changed after the installation and are still compliant if untouched?

I have no quarrel with doing that and won't pretend to know what anyone's motive might be.

I do think it's a good idea to use the current code and even the next version that will be adopted as a pole star to orient us in the proper direction so we can chose the proper path when making repairs to older systems. Grandfathering older sytems forward is necessary for practical reasons but it doesn't intend to imply that those non-compliant areas are to be considered off limits. Every honest effort should be toward bringing them into safe compliance when the situation arises.

joe-nwt

· #17 · Nov 16, 2020

surferdude2 said:
I have no quarrel with doing that and won't pretend to know what anyone's motive might be.

I do think it's a good idea to use the current code and even the next version that will be adopted as a pole star to orient us in the proper direction so we can chose the proper path when making repairs to older systems. Grandfathering older sytems forward is necessary for practical reasons but it doesn't intend to imply that those non-compliant areas are to be considered off limits. Every honest effort should be toward bringing them into safe compliance when the situation arises.

I would point out that the NEC considered those older systems safe and compliant at the time of installation. Can you make them safer? Absolutely. Does it make them unsafe if you don't? That's the $1,000,000.00 question.

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