Water heater 29 amps

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cadpoint

Senior Member
Location
Durham, NC
since you looked at see 422.13
also look at 210.20(A) continuous and non continious loads, for that correct understanind of why one would use 125%.
 

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
EEC said:
This wh label reads 29 amps, can you use 30 amp breaker?

Does the label say "minimum fuse or breaker size 29 amps" or does it say that it draws 29 amps ? most of them I've seen have a KW rating on them that is what I would use to figure breaker size.
 

cschmid

Senior Member
I believe it would trip under the right circumstances..like if they were taking a shower, doing laundry and running the dishwasher all in lets say an hour were the water heater would run non stop for 90 minutes or so..I believe the extra resistance caused by the extended heating time could cause the breaker to trip..then add in the age of the water heater and the hardness of the water to acerbate the whole scenario..
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
cschmid said:
I believe it would trip under the right circumstances..like if they were taking a shower, doing laundry and running the dishwasher all in lets say an hour were the water heater would run non stop for 90 minutes or so.
It still shouldn't trip even after 12 hours at 29a.
 

iwire

Moderator
Staff member
Location
Massachusetts
A standard 30 amp breaker should be able to pass 30 amps for 3 hours or 24 amps forever. However the mass produced molded case breakers are not IMO made that accurate and have bit of range on either side of the rating.

At 29 amps I would not try to guess if a 30 amp breaker will trip, it certainly might or it might not.

To many variables to consider, ambient temp, is it surrounded by other breakers or on it's own etc.

I sure would like to know more about the type of water heater under discussion.
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
Why would you risk this ? If your voltage is on the high side it will be more than 29 amps.Are you trying to use 10-2 romex ?What exactly is this water heater and how is it used.The kw rating is most important and the voltage rating that was stamped.
 

jrannis

Senior Member
cschmid said:
I believe it would trip under the right circumstances..like if they were taking a shower, doing laundry and running the dishwasher all in lets say an hour were the water heater would run non stop for 90 minutes or so..I believe the extra resistance caused by the extended heating time could cause the breaker to trip..then add in the age of the water heater and the hardness of the water to acerbate the whole scenario..

You really got me with the "extra resistance" thing, that was good.:grin:
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
cschmid said:
I believe it would trip under the right circumstances..like if they were taking a shower, doing laundry and running the dishwasher all in lets say an hour were the water heater would run non stop for 90 minutes or so..I believe the extra resistance caused by the extended heating time could cause the breaker to trip..then add in the age of the water heater and the hardness of the water to acerbate the whole scenario..

I am not following your idea.How does that change resistance ?
 

cschmid

Senior Member
I am just hypothetically adding to the situation..I assume that this is a decent sized residential hot water heater..I would have no issue with the 30amp breaker on it except were does the 29 amp figure come from..I have no idea..

Yet I do know after years of running a circuit maxed out the wire begin to deteriorate and the resistance then starts to change..like when your red wires are turning brown..have you ever measure the wire temp of a heater element that has been on for extended period of time..If you have a continuous duty water heater you should up size your wires due to the derating that should be used due to the extended run time..

is this necessary no is it required no..I am just saying you need to take into account the actual usage of the heater..

last time I checked resistance + voltage causes heat..the element is a fixed Resistance but the wires, connection points, thermostats, relays, etc.. have adjustments that need to be made for ambient temps..

continuous duty in an enclosed area will change the ambient temp and the ambient temp of the room and it environment has an effect..like the elements being all scaled over..so it is plausible I believe to trip a 30 amp breaker with a 29 amp load but it is going to take some added help from everything..yet I believe the unit will be several years old and had poor maintenace..I do not believe the question had any type of limitations on it...

if you want the math to prove it then I will have to say nope you could never trip it..
 

ItsHot

Senior Member
apartment upgrade

apartment upgrade

I was doing old apartment upgrades. The exsisting water heaters were 2 element heaters on 2 pole 20a breakers! This was the first time that I had seen this. Put my meter on a couple of panels to check voltage, it averaged around 245v.
 

cadpoint

Senior Member
Location
Durham, NC
Just an underlining thought, MHO!

Nothing againest a person asking any question, here, now, or in the future! I think where all here to expand our horizons. :rolleyes:

I know there's quite a few electrical quarks that we all run into daily.
Its not much so much as what we'd like to do, or ponder a particular application.

Its what?s required that is in the book. If you forget try re-reading
90.1 Purpose, (A) Practical Safeguarding, (B) Adequacy.

We might not know it, me might or might not agree with it, AHJ included.

But a lack of understanding of what is required is a disservice by any installer and only another bad mark verses properly representing our trade.
Theirs plenty of ways to cheat, I'm not here for all that...

Sorry to RANT, I'll go burn some energy someplace else, for awile...
 

jetlag

Senior Member
EEC said:
This wh label reads 29 amps, can you use 30 amp breaker?

Is this a comercial w/h ? a 4500 watt residential w/h usually reads about 18 amps. Ive never seen a residential w/h you couldn't run on #10 wire. Id be afraid to use it on that one. That one needs a 40 a breaker and # 8 cu. It might not be continuous all the time but there will be times when the w/h will be ran continuous and the breaker and wire should be rated 80 %.
 

M. D.

Senior Member
Jim W in Tampa said:
I am not following your idea.How does that change resistance ?

As the temp of the wire increases so does the resistance more resistance equals more heat which adds to the resistance again creating more heat,.. and with this not being sized at 125% it could indeed trip.
 
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