20 amp breaker for water heater

[jfrederick (Joshua Frederick)]

20 amp breaker, with 10 gauge wire, installed on 50 gal. Whirlpool heater (upper left breaker).

Comments?

Thanks in advance.

[rmeier2 (Robert Meier)]

Probably too small but what is the heater wattage?

[jfrederick (Joshua Frederick)]

@Robert_Meier

Probably too small but what is the heater wattage?

I’m assuming 4500, no? Isn’t that typical for newer, 50 g electric? Not 100% sure, though.

[rmeier2 (Robert Meier)]

If it’s 4500 then the 20 amp will work but it won’t be code compliant. A water heater of this type is required to be considered a continuous load meaning that the branch circuit needs to be calculated at 125% of the heater’s rated ampacity.

4500/240 = 18.75 amps, will work on a 20 amp OCPD but,
18.75*125% = 23.4 amps, requires a 25 or 30 amp circuit.

[mchiquete (Mary Ann Chiquete)]

@Robert_Meier

If it’s 4500 then the 20 amp will work but it won’t be code compliant. A water heater of this type is required to be considered a continuous load meaning that the branch circuit needs to be calculated at 125% of the heater’s rated ampacity.

4500/240 = 18.75 amps, will work on a 20 amp OCPD but,
18.75*125% = 23.4 amps, requires a 25 or 30 amp circuit.

Great information Robert, thanks.

[ccurrins (Christopher Currins, CMI)]

Here’s a good link, I like it anyway.

How to figure Volts-Amps-Watts for residential water heater

[rmeier2 (Robert Meier)]

@mchiquete

Great information Robert, thanks.

You’re welcome, here’s a few NEC sections to accompany my last post:

422.11 Overcurrent Protection. Appliances shall be pro-
tected against overcurrent in accordance with 422.11(A)
through (G) and 422.10.
(E) Single Non–motor-Operated Appliance. If the branch
circuit supplies a single non–motor-operated appliance,
the rating of overcurrent protection shall comply with the
following:
(1) Not exceed that marked on the appliance.
(2) Not exceed 20 amperes if the overcurrent protection
rating is not marked and the appliance is rated
13.3 amperes or less; or
(3) Not exceed 150 percent of the appliance rated current if
the overcurrent protection rating is not marked and the
appliance is rated over 13.3 amperes. Where 150 per-
cent of the appliance rating does not correspond to a
standard overcurrent device ampere rating, the next
higher standard rating shall be permitted.

422.13 Storage-Type Water Heaters. A fixed storage-type
water heater that has a capacity of 450 L(120 gal) or less shall
be considered a continuous load for the purposes of sizing
branch circuits.

[jwhitt (Joseph M. Whitt)]

My 40 gallon has been on a two pole 20 for more than 5 years with no problem.

[jmcgrail (James T. McGrail, HI-3097)]

Great link !

[tjorge (Travis Jorge)]

@Robert_Meier

If it’s 4500 then the 20 amp will work but it won’t be code compliant. A water heater of this type is required to be considered a continuous load meaning that the branch circuit needs to be calculated at 125% of the heater’s rated ampacity.

4500/240 = 18.75 amps, will work on a 20 amp OCPD but,
18.75*125% = 23.4 amps, requires a 25 or 30 amp circuit.

I know this is old thread, but I have a setup for the same example above. Except in my case the breaker in the box is 30amp everything’s good there, but that circuit is run through a reliance transfer panel that is on a 20amp breaker when set to run on the generator. It uses 10 gauge wire all around so thats fine but i’m wondering if that 20amp breaker is an issue while set to generator. It doesn’t pop when running but I just want to be sure its safe.