7500W Heater Wire Sizing

Status
Not open for further replies.
T

turtlepokerman

Member
Location
Omaha
Greetings,
An electrician installed a #10AWG copper wire in my garage for a future electric garage heater. The heater that is sized for the space should be 7500W. When I asked the electrician if the wire would be appropriately sized to power the heater, he mentioned that the wire is appropriately sized and to use a 30A breaker. I came back with the calculations of 7500/240V (Heater Rated Voltage) = 31.25A, so I didn't see how that would work. Then he came back and told me to use a 35A breaker and I would be fine. I'm now concerned that I will not be in compliance with 240.4(D). Can anyone confirm if a 35A Breaker is allowed to protect a #10AWG CU wire being utilized for a garage heater per NEC 2017?
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Space heating branch circuits are considered a continuous load (424.3)by the NEC so your circuit requirement is 40 amps. Forget the #10
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
A 35 amp OCPD on the #10 conductors would not be code compliant for a heater. As Augie stated the 125% rule furthers the argument that the #10's are too small.
 
T

turtlepokerman

Member
Location
Omaha
Try to answer all your questions in one post:
*Good catch on the 424.4(B) requirement. This is a fixed heater. I was wondering if it would be running for more than 2 hours, but 424.4(B) makes it clear that it is considered a continuous load.
*Yes, licensed Master Electrician.
*I was thinking that a #8AWG Copper Conductor on a 40A breaker would be adequate.
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
There is a bit of confusion here.

The wire was installed for a _future_ heater. The electrician stated that the wire was sized to be protected by a 30A breaker, which is correct.

This is sufficient for a 5700W heater.

Is it possible that the electrician installed a too small wire because at the time of installation the size of the heater was not properly known?

The statement that you would be fine with a 35A breaker is not code compliant.

-Jon
 
T

turtlepokerman

Member
Location
Omaha
winnie said:
There is a bit of confusion here.

The wire was installed for a _future_ heater. The electrician stated that the wire was sized to be protected by a 30A breaker, which is correct.

This is sufficient for a 5700W heater.

Is it possible that the electrician installed a too small wire because at the time of installation the size of the heater was not properly known?

The statement that you would be fine with a 35A breaker is not code compliant.

-Jon
Click to expand...

Winnie,

You are correct at the time of the installation the heater size was unknown. All that was written in the contract was to supply a garage heater circuit. When we received the sizing requirements, we found out that the heater needed to be at least 7200W which is not a standard space heater size so it went up to a 7500W Heater. We called back the electrician and asked them the questions in the initial post on if a 7500W heater could be run from the #10 wire that they had pulled. The answer was yes from the electrician. We then pursued with the following questioning on the 30A Breaker sizing being inadequate. In which we were told to use a 35A breaker which eventually lead to this thread.

My perspective of the situation: The general contractor should have specified the heater sizing requirements to the electrican when the original contract was signed. When we followed up with the electrician on putting an appropriately sized 7500W heater in the garage, the electrician should have replied that the circuit they pulled was inadequate for that size of heater.
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
So now you have several options:

1) Change the heater requirements. If you _insulate_ the garage, then the calculated heat load will be lower and you can install a smaller heater.

2) Change the circuit. You can replace the circuit with #8 conductors, and use a 40A breaker.

3) Change the type of heater used. A heat pump will use less power for the same heating, but at higher up front cost and you need to be careful that you have sufficient heat on the coldest days.
 
infinity

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
turtlepokerman said:
Winnie,

You are correct at the time of the installation the heater size was unknown. All that was written in the contract was to supply a garage heater circuit. When we received the sizing requirements, we found out that the heater needed to be at least 7200W which is not a standard space heater size so it went up to a 7500W Heater. We called back the electrician and asked them the questions in the initial post on if a 7500W heater could be run from the #10 wire that they had pulled. The answer was yes from the electrician. We then pursued with the following questioning on the 30A Breaker sizing being inadequate. In which we were told to use a 35A breaker which eventually lead to this thread.

My perspective of the situation: The general contractor should have specified the heater sizing requirements to the electrican when the original contract was signed. When we followed up with the electrician on putting an appropriately sized 7500W heater in the garage, the electrician should have replied that the circuit they pulled was inadequate for that size of heater.
Click to expand...
Yes the circuit is too small for the heater that no one knew what the size was before the sparky pulled the wire. Other than he saying to use a 35 amp OCPD on the #10 conductors I don't see how the electrician did anything wrong.
 
T

turtlepokerman

Member
Location
Omaha
infinity said:
Yes the circuit is too small for the heater that no one knew what the size was before the sparky pulled the wire. Other than he saying to use a 35 amp OCPD on the #10 conductors I don't see how the electrician did anything wrong.
Click to expand...
Yes I agree. The electrician did nothing except first tell me that a 30A Circuit would be acceptable and then tell me after I questioned it that a 35A Breaker would be acceptable on a #10AWG CU wire. I more posted this to the forum to make people aware to check wire sizing before purchasing a space heater and to ask what size of space heater is required for the space, before pulling a circuit.
 
kwired

kwired

Electron manager
Location
NE Nebraska
turtlepokerman said:
Yes I agree. The electrician did nothing except first tell me that a 30A Circuit would be acceptable and then tell me after I questioned it that a 35A Breaker would be acceptable on a #10AWG CU wire. I more posted this to the forum to make people aware to check wire sizing before purchasing a space heater and to ask what size of space heater is required for the space, before pulling a circuit.
Click to expand...
Many times a garage gets a 5000 watt heater. It may not be enough heat to use the space it like it were a living room, but is generally plenty for keeping above freezing on the coldest of winter days.

But as mentioned your electrician was wrong once he said it would be ok to put a 35 amp breaker on it.
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Greentagger said:
Lets hope it would trip.
Click to expand...

One would think, but take a look at a common breaker trip curve:

The long duration trip point is anywhere between 1x and 1.3x the rating. Run 31A through a 30A breaker and there is a very good chance it wouldn't trip. Add to the the heater cycling on and off....

However it would likely run hot and suffer long term damage.

This expected trip curve tolerance is probably one of the reasons for the 'small conductor' rules.

-Jon
 
mbrooke

mbrooke

Batteries Included
Location
United States
Occupation
Technician
turtlepokerman said:
Yes I agree. The electrician did nothing except first tell me that a 30A Circuit would be acceptable and then tell me after I questioned it that a 35A Breaker would be acceptable on a #10AWG CU wire. I more posted this to the forum to make people aware to check wire sizing before purchasing a space heater and to ask what size of space heater is required for the space, before pulling a circuit.
Click to expand...

Is he from, or as he worked in Canada?
 
mbrooke

mbrooke

Batteries Included
Location
United States
Occupation
Technician
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I think petersonra's point was that this 7500W heater would likely not trip the breaker on overload.

If you are talking sahort circuit protection, then yes, it would trip.

-Jon
 
mbrooke

mbrooke

Batteries Included
Location
United States
Occupation
Technician
winnie said:
I think petersonra's point was that this 7500W heater would likely not trip the breaker on overload.

If you are talking sahort circuit protection, then yes, it would trip.

-Jon
Click to expand...


Agree. But 31 amps is pushing it, 125% would be a better option. And meet Code in the CEC.

Though yes, breaker won't trip in reality at 31 amps :)

However modern breaker trip curves are getting closer and closer to their handle rating.
 
Status
Not open for further replies.
Top