water heater

[bphgravity]

Re: water heater

Originally posted by howlev:
my point is why do I have to use anything greater then a 20A breaker

Because that would only be 107% of the rating of the appliance. 422.13 requires 125%.

 

[howlev]

Re: water heater

210.3 says that the o.c.d determins the circuit rating not the branch circuit rating you can have a 500mcm for voltage drop or a #12 wire @60C for a 25A branch circuit conductor and you still have an 18.75A load on a 4500 watt water heater as per 422.11E 3 which is the specified circuit rating for art 210.3 art. 240.4 states you can not size your o.c.p. greater then 20A for #12 I have already derated my conductors as the thhn conductors are rated at 90C and they are being used at 60C rating this is not a continous load therefore I see no need to oversize my o.c.p.even though I can if I so choose up to 150%

 

[bphgravity]

Re: water heater

Originally posted by howlev:
210.3 says that the o.c.d determins the circuit rating not the branch circuit rating...

So what circuit do you think the code is refering to if not the branch circuit?


Also, since you are totally ignoring the requirement of 422.13, what is this section for?

[ May 25, 2004, 05:22 PM: Message edited by: bphgravity ]

 

[iwire]

Re: water heater

We have given you the code articles, it is very clear and straight forward.

What exactly would be the point of 422.13 in your interpretation?

 

[howlev]

Re: water heater

422.10 capable of carrying"appliance current" without overheating appliance current is 18.75

 

[gpedens]

Re: water heater

Howlev, the best reason for using something greater than a 20 amp breaker, is the the owner wanting to know why his water heater breaker keeps tripping. It has been my experience that molded case breakers aren't precison pieces of equipment. They are subject to trip 10% or more less than their value. A 20 amp breaker might trip at 17 or 18 amps or it might trip at 22 or 23. Using a 20 amp breaker will protect the water heater but there is a possibility it wont make the home owner happy. The 25% greater than nameplate OCPD requirement covers the lack of precision in the molded case breaker.

 

[howlev]

Re: water heater

I think you would get an argument from not only the breaker man. but also UL but either way what does the code say I will tell you that I have a 4500 watt w.h with a 20 breaker for the last 2 years and never had a problem I have also installed many like this also without a problem.

 

[don_resqcapt19]

Re: water heater

howlev,

I have also installed many like this also without a problem

That doesn't chage the code rules. The code is clear here and this circuit must have a 25 amp OCPD.

210.3 says that the o.c.d determins the circuit rating not the branch circuit rating

210.3 says branch circuit rating, not circuit rating!

210.3 Rating.
Branch circuits recognized by this article shall be rated in accordance with the maximum permitted ampere rating or setting of the overcurrent device.

Don

 

[bphgravity]

Re: water heater

This is a quote from an article on branch circuit wiring and OCD sizing written by Brian McPartland from the Informer Newsletter

...Also worth noting is what UL has to say regarding this matter. Throughout many discussions with UL personnel about this issue, each and every one has indicated that "how" these overloaded devices will fail is unknown. They may fail violently and explode. They may simply not operate. They may burst into flame or perform in other unknown ways. Each and every one of the UL personnel with whom I discussed this matter said that failure is inevitable. Remember: A small overload, a long time failure. A large overload, a short time failure. But in either case, failure of the device will occur.

 

[howlev]

Re: water heater

I have just re read art.210.3 and 422.13 I have also contacted NFPA for an interpretation At this point I believe that 210.3 does not apply as the FPN for 422.13 refers you back to 422.10 for your branch circuit rating where there is no mention of the o.c.d determining the rating of the branch circuit.but 210.2 does not address this Will post the NFPA decision asap

 

[peter d]

Re: water heater

Howlev,


If I may....

Some very talented and knowleable people have answered your question. All due respect, it appears you are using circular reasoning to justify using an undersized breaker and conductors.

 

[gpedens]

Re: water heater

Howlev, try this explanation from Square D. http://ecatalog.squared.com/pubs/Circuit%20Protection/Circuit%20Breaker%20Trip%20Units/0100DB0101.pdf
Basically it says their breakers are designed for a continuous load of 80% of the breaker rating. The 80% is taken from the inverse of 125% (1/1.25=0.8) from NEC 210.20a. In their example for the standard 40 degree C rating a 400 amp breaker can be used on a 320 amp load. Now that translates to a 16 amp load for a 20 amp breaker. It also goes on to say that if the ambient temp is 10C that 400 amp breaker is rated at 500 amps, but you can only use it in a 0.8x500 or a 400 amp circuit. You are correct in that it probably wont trip in most cases, however in mine the ambient temp can be on the high end and you get that occasional trip. Breakers are designed for continuous load to cover a broad range of use. If the breaker is not listed for 100% load you can only use it at 80% of its rating for continous use. There are breakers listed for 100%, but most are not. If the 20 amp breaker you are using is part of the water heater assembly is is ok. At higher temperatures the 400 amp breaker is no longer rated at 400 amps. That is what I was trying to tell you about breaker time current curves. The above link probably explains it better. Use the 25 amp breaker. The 30 is a little overkill but it may be right for the replacement water heater. Seems like my water heater has 5000 watt elements.

 

[don_resqcapt19]

Re: water heater

howlev,

Will post the NFPA decision asap

A formal interpretation from the NFPA takes months. A statement by a NFPA staff member is just an opinion and no more valid than yours or mine.
Don

 

[howlev]

Re: water heater

Don it's not what you know it's who you know I will probably have a formal interpretation within a day or two

 

[ryan_618]

Re: water heater

You do realize that the members of the code making panels are the only ones who can create a formal interpretation, right? I think they are a little bit busy right now, you know, voting on the 2005 NEC over the next few days. In fact, come to think of it, I ate breakfast with one of them this morning. I don't think your going to get a formal interpretation in "a day or two", but give it a shot I guess!

 

[roger]

Re: water heater

Howlev,

Originally posted by howlev:
Don it's not what you know it's who you know I will probably have a formal interpretation within a day or two

Will you be able to get a two day turn around on all issues that arrise here?

I think the ability to do this will set this forum on top of the electrical world.

Roger

 

[don_resqcapt19]

Re: water heater

howlev,

Don it's not what you know it's who you know I will probably have a formal interpretation within a day or two

Then it will not be a formal interpretation. A formal interpretation, requires a ballot by mail of the members of the code making panel that has responsibility for the section in question.

Responses to requests for interpretation are provided by NFPA staff on an informal basis. This allows a timely response that in almost all cases adequately addresses the need for information. A request for an interpretation may, however, be processed on a more formal basis if so desired. This involves balloting the responsible NFPA technical committee, and requires an extended processing time and may not result in an answer if consensus cannot be established. This is referred to as a "Formal Interpretation", and it is used in only limited cases. Refer to Section 6 of the NFPA Regulations Governing Committee Projects.

Don

[ May 26, 2004, 07:02 AM: Message edited by: don_resqcapt19 ]

 

[a.wayne3@verizon.net]

Re: water heater

The post about 210.3 is a good point where is there a 25 35 45 ...... listed.So the next 10 factor breaker size should be what is required.A 30.We just had this issue in the last 6 months.What it came down to was that If You go 125 % over the rating of an appliance.You have to take into consideration the 80% of a breaker rating.That`s why it`s there.Do you factor it in at 125% or do you go by kw x 100 divided by voltage,and that`s the circuits ocpd.No 25 listed in the code book go by 10`s.30 next size ocpd. Simple.

 

[a.wayne3@verizon.net]

Re: water heater

Sorry forgot to add this is all contingent on what raceway you have NM /Pipe ?NM use 10 for pipe at 25 all`s good to go.

 

[a.wayne3@verizon.net]

Re: water heater

Damn I`m getting old.... For 25 amp. in pipe #12 IS OK........