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Minimum size NM cable for water heater

david luchini said:
It doesn't ask for the Minimum size breaker. One could infer that it is asking for the maximum size breaker.
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I read the statement I replied to as saying that nothing was asked about a breaker. Maybe he was trying to say that minimum wasn’t asked.

I wonder if the question was multiple choice? If so, there was likely only one correct answer.
 
The question "What size circuit breaker with 60/75C wire terminations will protect this circuit?"

Should read something like "If the manufacturer does not include a maximum overcurrent protection in the installation instructions what is the maximum size breaker with 60/75C wire terminations permitted to protect this circuit?"
 
wwhitney said:
Sure, but the second question in the OP (first image) doesn't ask for the minimum, only the first question does.

Cheers, Wayne
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Yes I know but I still wanted to know because it is apparent that more than one correct answer could be used
 
tortuga said:
The question "What size circuit breaker with 60/75C wire terminations will protect this circuit?"

Should read something like "If the manufacturer does not include a maximum overcurrent protection in the installation instructions what is the maximum size breaker with 60/75C wire terminations permitted to protect this circuit?"
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So if the manufacture instructions call for a specific breaker you must follow this regardless of calculations or other NEC codes you may come across, correct?

If no breaker size provided you must do the calculations. Usually the size of the breaker is on the paper manual but not often the nameplate?
 
Jpflex said:
So if the manufacture instructions call for a specific breaker you must follow this regardless of calculations or other NEC codes you may come across, correct?
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No, you have to comply with both. If the manufacture specifies a breaker size that is contrary to the allowances of the NEC, they have just created a product that can't be installed in jurisdictions that use the NEC.

Cheers, Wayne
 
tortuga said:
Most 50 gallon 4500W resistance waterheater's we see (and they are quite common here) if not all come with instructions that say to use a 25A breaker for 240V, which is why supply houses stock 2 pole 25's but you don't see two pole 35's or 45's stocked. So either 110.3(B) and/or not voiding the warranty they usually end up on a 25A breaker.
Years ago I worked with a guy that tried to argue with an inspector you could use #12 MC on a 25A breaker to a 4500W waterheater, he lost that argument.
Read the test questions carefully and just focus on what its asking.
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Ok. Mc cable # 12 AWG cannot be on a 25 ampere breaker because of 240.6D? small conductor OCPD code rule correct?

However, as you probably know this doesn’t apply to motors which can use a smaller ampacity branch circuit wire than the larger ampacity breaker 250% of FLC current
 
wwhitney said:
No, you have to comply with both. If the manufacture specifies a breaker size that is contrary to the allowances of the NEC, they have just created a product that can't be installed in jurisdictions that use the NEC.

Cheers, Wayne
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But I thought NEC code made manufacture listed instructions overrule NEC general wiring methods?
 
wwhitney said:
No, they can only add additional requirements (via 110.3(B)), not relive you of an NEC requirement.

Cheers, Wayne
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So if a manufacture is found to be wrong in their instructions, do I call their engineer to acknowledge their error to be certain or if I mistake them to be wrong and follow NEC then it seems to be a big complication
 
Jpflex said:
However, as you probably know this doesn’t apply to motors which can use a smaller ampacity branch circuit wire than the larger ampacity breaker 250% of FLC current
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I look at it as a larger OCPD, not a smaller conductor size.
 
I would not violate a NEC rule. if there is a question contact the manufacturer and then discuss it with the AHJ. In many decades of doing this I can't recall a instance where listed equipment was contrary to the NEC. UL, NEMA, and the NEC play well together
 
The water heater manufacturers specs are typically equal to or lower than what the NEC allows (see attached instructions from one) A long time ago there was a small house 'fire' involving a water heater on a 30A breaker that did not trip, the manufacturer got absolved of any damages by saying the installer did not follow the installation instructions requiring a 25A breaker.
 

Attachments

  • waterheater-smaller.jpg
    waterheater-smaller.jpg
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augie47 said:
I would not violate a NEC rule. if there is a question contact the manufacturer and then discuss it with the AHJ. In many decades of doing this I can't recall an instance where listed equipment was contrary to the NEC. UL, NEMA, and the NEC play well together
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A lot of times an appliance nameplate will list an ampere rating but won’t specify if this is the OCPD required or the nameplate FLA running current load. I assume the ampere rating refers to the latter.

However, if the nameplate marking were to show both how would you distinguish the manufacturer’s listed OCPD value not to be exceeded. Will it clearly say max overcurrent protective device, breaker or fuse?

I haven’t seen this on labels I’ve encountered?
 
Jpflex said:
A lot of times an appliance nameplate will list an ampere rating but won’t specify if this is the OCPD required or the nameplate FLA running current load. I assume the ampere rating refers to the latter.

However, if the nameplate marking were to show both how would you distinguish the manufacturer’s listed OCPD value not to be exceeded. Will it clearly say max overcurrent protective device, breaker or fuse?

I haven’t seen this on labels I’ve encountered?
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It also gets confusing when to treat a motor appliance according to NEC article covering motors or under article for appliances.

I guess some examples of this could be motor operated kitchen waste disposers or appliance air compressors.

At this point I believe you are to not exceed the air compressors nameplate listed OCPD rating according to appliance rules BUT if not stated on name plate, you then base the OCPD rating on article NEC regarding motors? (FLC and HP tables)
 
LarryFine said:
This discussion could apply to 40a vs 50a range circuit breakers, too.
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Yea I had confusion on the subject of ranges since the company I worked for once told me to wire up a receptacle for a range/ stove but they themselves had not yet purchased the range nor had any idea the size in watts it would be for a non residential employee kitchen and expected me to just know.

I explained it would help if I knew the range WATTS/VA but the boss just told me to go big so I decided to install a number 6 AWG NM cable conductor and hope for the best

The company often worked in this way by them deciding the main panels or sub panels ampacity and feeders before knowing all loads to be served (without load calculation) while piling on loads later on
 
Jpflex said:
Ok. Mc cable # 12 AWG cannot be on a 25 ampere breaker because of 240.6D? small conductor OCPD code rule correct?

However, as you probably know this doesn’t apply to motors which can use a smaller ampacity branch circuit wire than the larger ampacity breaker 250% of FLC current
Click to expand...
For this discussion on this water heater. You are correct.
The ** in the note at the bottom of the ampacity table refers you to 240.4.

240.4. (D) is what I think you meat to type.

I like to have the guys write in at that note.
" See 240.4(D) Unless permitted in 240.4 (E) or 240.4 (G)."
 
Tulsa Electrician said:
For this discussion on this water heater. You are correct.
The ** in the note at the bottom of the ampacity table refers you to 240.4.

240.4. (D) is what I think you meat to type.

I like to have the guys write in at that note.
" See 240.4(D) Unless permitted in 240.4 (E) or 240.4 (G)."
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I’m going from what i can remember as i left my code book at work 3 hours away. Unfortunately i cannot look up code accurately without it so im going off of what i can recall. The company lost investor funding and so I’ve been laid off “temporary” yesterday. For this reason I’ll be doing a lot more studying
 
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