HPWH on a "Dedicated Circuit" or a "Shared Circuit"

M

Mister.Soda

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Location
Boulder, CO
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Engineering Consultant
I have a client who is replacing a gas water heater in their utility room with a HPWH. The appliance branch circuit currently only feeds a washing machine that has a max power draw of ballpark 5A (slightly less). The branch circuit has a 20A breaker, is run on 12/2 wire, but interestingly, appears to only have 15A sockets.

Rheem makes two categories of 120v HPWH: one designed for shared 15A circuits (390 - 440W) and one designed for dedicated circuits (1100W). (Both mfr specs. I don't have access to the nameplates yet.)
The home outlets run at about 124V. In my mind, the 440W HPWH will draw about 3.7A (<4) and the 1100W ~9.2A (<10).
The 1100W version is preferable because of more than 2x faster recovery rates.

The 440W, <4A HPWH is a no-brainer, obviously fine. The question is, can the <10A HPWH be installed on this shared branch circuit?

NEC 422.13 indicates that a storage type water heater of 120 gallons or less shall be considered a continuous load, which requires a 125% continuous use factor for load calculations. And NEC 210.23(A)(2) says that on a multi-outlet branch circuit, the rating of cord-and-plug connected equipment fastened in place (like a water heater) shall not exceed 50% of the branch circuit rating, where lighting units or portable cord-and-plug connected equipment are also supplied from the branch circuit.

Without the 125% multiplier, the <10A HPWH should be fine on the circuit. When the HPWH and washer both run at full power, they're still drawing less than 15A.

However, my concern is that 125% multiplier. With the 125% multiplier, 9.2A becomes 11.5A, which exceeds the 50% limit of a multi-outlet branch circuit.

Client has a strong preference for the 1100W unit. I'm fine putting <15A of equipment on the 20A circuit, but am a bit shaky on whether this would pass code or not. Probably not? Interested in thoughts and feedback.

Cheers.
 
Mister.Soda said:
The branch circuit has a 20A breaker, is run on 12/2 wire, but interestingly, appears to only have 15A sockets.
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This is normal, both 15A and 20A receptacles are rated for use on 20A branch circuits, and within the same grade of receptacle, the only difference is the shape of the holes in the receptacle face plate. So unless you have a piece of equipment with a 20A plug on it, there's no reason to ever use 20A receptacles.

As to your primary question, if you add an enclosed 15A circuit breaker next to the HPWH, that creates an individual branch circuit for it. E.g. Square D QO2L30SCP. Still need to check the nameplate of the 120V dedicated circuit HPWH and the washer to ensure that 20A is sufficient for the load.

Cheers, Wayne
 
By the technical letter of the code you would be in violation. But also I wouldn't lose any sleep over it either
 
Thank you all so far.

@wwhitney ,
wwhitney said:
This is normal, both 15A and 20A receptacles are rated for use on 20A branch circuits, and within the same grade of receptacle, the only difference is the shape of the holes in the receptacle face plate. So unless you have a piece of equipment with a 20A plug on it, there's no reason to ever use 20A receptacles.

As to your primary question, if you add an enclosed 15A circuit breaker next to the HPWH, that creates an individual branch circuit for it. E.g. Square D QO2L30SCP. Still need to check the nameplate of the 120V dedicated circuit HPWH and the washer to ensure that 20A is sufficient for the load.

Cheers, Wayne
Click to expand...
I hadn't considered this, but love this idea. I'll definitely dig into this more.

@infinity ,
I'm interested as to why. NEC 422.13 and 210.23(A)(2) seem to explicitly allow it. I'm curious if there are other clauses or provisions that explicitly disallow it. Can you point me to them?

@suemarkp , It's a single utility room. The current water heater is a stand-alone gas unit with no plug. The proposed system, either one, would be a cord-and-plug unit. No hardwiring of the HPWH.
 
Mister.Soda said:
I'm interested as to why. NEC 422.13 and 210.23(A)(2) seem to explicitly allow it. I'm curious if there are other clauses or provisions that explicitly disallow it. Can you point me to them?
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As infinity mentioned, see 210.11(C)(2). If this utility room is the only laundry area in the dwelling, then the receptacle for the washer is the 210.52(F) receptacle.

Of course, nothing says (that I'm aware of) that you can't plug your HPWH into the laundry receptacle. But then you are back to the issues in the OP, of both appliances on the same branch circuit. Biggest problem I see would be if the instructions on the 1100W HPWH call for an individual branch circuit--in that case you can't put them on the same branch circuit. If it doesn't, you could get around the 210.23(A)(2) issue by fastening the washer in place. : - )

Now you could turn the 20A branch circuit into a feeder by setting a small panel with two spaces, one for a laundry branch circuit and one for an individual branch circuit for the HPWH. But now you have a load calculation issue, as the laundry branch circuit is to be considered at 1500 VA per 220.52(B). So that leaves only 900VA for your HPWH, even if the actual washer supplied is only 600 VA as you indicate in the OP.

Mister.Soda said:
NEC 422.13 indicates that a storage type water heater of 120 gallons or less shall be considered a continuous load, which requires a 125% continuous use factor for load calculations. And NEC 210.23(A)(2) says that on a multi-outlet branch circuit, the rating of cord-and-plug connected equipment fastened in place (like a water heater) shall not exceed 50% of the branch circuit rating, where lighting units or portable cord-and-plug connected equipment are also supplied from the branch circuit.
Click to expand...
Since 210.23(A)(2) uses the word "rating" rather than load, you could argue that the rating does not get a 125% continuous use factor. However, you really need the actual nameplate data on your two loads.

But it seems like your best solution is to run a new branch circuit for the HPWH.

Cheers, Wayne
 
Thanks All! Really good stuff.

210.11(C)(2)
In addition to the number of branch circuits required by other parts of this section, at least one additional 20-ampere branch circuit shall be provided to supply the laundry receptacle outlet(s) required by 210.52(F). This circuit shall have no other outlets.

210.52(F)
In dwelling units, at least one receptacle outlet shall be installed in areas designated for the installation of laundry equipment.

So 210.52(F) says the utility room (laundry room) must have at least one receptacle outlet for laundry equipment.
210.11(C)(2) says that single receptacle can have more than one outlet ["outlet(s)"] but that circuit shall have no other outlets.

The current laundry receptacle is a duplex receptacle, featuring two outlets. The "shared circuit" HPWH could totally be connected to the second socket. No probs.

It seems to me the >9A HPWH shouldn't be connected to the same circuit, though there are probably a few fuzzy dirty work arounds, and some of these might even create some distant long-term risks. I don't typically base my work on cutting corners or fuzzy boundaries.

Thanks for all your help.
 
Mister.Soda said:
The current laundry receptacle is a duplex receptacle, featuring two outlets.
Click to expand...
In NEC speak, this is not correct. An "outlet" is anywhere you hook up your utilization equipment to the building wiring. Doing that via a receptacle is common, but some utilization equipment is hardwired--that connection is still an outlet. A "receptacle" is a single contact device to mate with a plug. A "duplex receptacle" is two receptacles on a single yoke. And a "receptacle outlet" is an outlet at which you have installed a receptacle for the purpose of connecting your utilization equipment. See Article 100 for the exact definitions, but the above is the gist.

With those clarifications in mind, the import of several of the sections you've quoted so far in the thread are likely a bit different than you first thought.

Cheers, Wayne
 
wwhitney said:
In NEC speak, this is not correct. An "outlet" is anywhere you hook up your utilization equipment to the building wiring. Doing that via a receptacle is common, but some utilization equipment is hardwired--that connection is still an outlet. A "receptacle" is a single contact device to mate with a plug. A "duplex receptacle" is two receptacles on a single yoke. And a "receptacle outlet" is an outlet at which you have installed a receptacle for the purpose of connecting your utilization equipment. See Article 100 for the exact definitions, but the above is the gist.

With those clarifications in mind, the import of several of the sections you've quoted so far in the thread are likely a bit different than you first thought.

Cheers, Wayne
Click to expand...
Ah. Ok. I think I had "receptacle" and "outlet" switched in my head, but that's actually better off.

210.52(F) says the laundry room should have at least one receptacle outlet, but may have more than one. (ie, it could have a two- or four-plug box).
210.11(C)(2) says that circuit shall not have any other outlets. (ie I couldn't hard wire a WH onto that circuit or split the circuit with a junction box and install a second receptacle outlet closer to the WH.

I still feel like I can plug a HPWH into the existing receptacle outlet(s) next to the washer and still be in compliance with both provisions, and with 210.23(A)(2).
 
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