Electric heat circuits

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Electric heat circuits

  • Yes

    Votes: 6 66.7%
  • No

    Votes: 3 33.3%
  • Only with unqualified personal

    Votes: 0 0.0%

  • Total voters
    9
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mbrooke

Batteries Included
Location
United States
Occupation
Technician
Ok new home build with electric heat. Baseboards total up to 4,800 watts and 6000 watts per circuit.


4.8kw circuits #14 with 25 amp OCPD

6kw circuits #12 with 35 amp OCPD



In reality is there a risk or any danger doing it this way?
 

Smart $

Esteemed Member
Location
Ohio
Whats the NEC's reasoning behind that? :huh:
The NEC [typically] does not provide reasons.

Speculation will likely say because small conductors are abused more often than larger conductors... and there's usually a lot more footage of small conductors.

As for requirements, see 240.4(D).
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
The NEC [typically] does not provide reasons.

Speculation will likely say because small conductors are abused more often than larger conductors... and there's usually a lot more footage of small conductors.

As for requirements, see 240.4(D).

240.4 (D) just restricts the over current protection to a value lower than the allowed current carrying capacity in 310.15 (B) (16). My understanding is that motor loads are exempt and are allowed to use the raw table value.
 

Smart $

Esteemed Member
Location
Ohio
240.4 (D) just restricts the over current protection to a value lower than the allowed current carrying capacity in 310.15 (B) (16). My understanding is that motor loads are exempt and are allowed to use the raw table value.
Yes, but the breaker/fuse at the supply end is only for short circuit and ground fault protection. Overload (which is comparable to standard overcurrent for other loads) has to be handled by another device... and its rating is usually comparable to the standard OCPD rating.

So what does that have to do with electric heat circuits?
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Yes, but the breaker/fuse at the supply end is only for short circuit and ground fault protection. Overload (which is comparable to standard overcurrent for other loads) has to be handled by another device... and its rating is usually comparable to the standard OCPD rating.

So what does that have to do with electric heat circuits?



Everything, why would fixed electric heat need overload protection to start with?
 

iwire

Moderator
Staff member
Location
Massachusetts
OK, seriously?

Lets imagine a element fault to ground near one end of the element, that could cause an overload by shortening the effective length and therefore lowering the resistance of the heater.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Everything, why would fixed electric heat need overload protection to start with?

I think in the case of a standard branch circuit the circuit breaker is really an overcurrent protector but is also an overload protector.

In the case of a motor the circuit breaker is , as Smart started, only for ground fault and short circuit as the motor has overload protection. This overload protection protects the 14 gauge wire when installed on a larger overcurrent protective device such as a 25 or 30 amp breaker.

You don't have this with baseboard heat so you must abide by 240.4(D)
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
OK, seriously?

Lets imagine a element fault to ground near one end of the element, that could cause an overload by shortening the effective length and therefore lowering the resistance of the heater.




True, and you may have a good point here, but I dont think I have ever seen a baseboard element shorted to ground. Isnt the niochrome wire imbedded in an insulating material? Even then I dont think all 8 baseboards will do it at once.
 

iwire

Moderator
Staff member
Location
Massachusetts
I think in the case of a standard branch circuit the circuit breaker is really an overcurrent protector but is also an overload protector.

I think the point he was trying to make is that when you have a circuit that is a designed for a specific fixed load you really do not need (outside of rules) overload protection. All you would need for safety is short circuit protection. This of course assumes the load can not increase.

It is worth noting that the nec already uses this type of concept when it comes to service conductors supplying more than one service disconnecting means. For example if you use the exception you can have 1,000 amps of wire 'protected' by 3,000 amps of OCP as long as the load calculations are under 1,000 amps.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I think the point he was trying to make is that when you have a circuit that is a designed for a specific fixed load you really do not need (outside of rules) overload protection. All you would need for safety is short circuit protection. This of course assumes the load can not increase.

It is worth noting that the nec already uses this type of concept when it comes to service conductors supplying more than one service disconnecting means. For example if you use the exception you can have 1,000 amps of wire 'protected' by 3,000 amps of OCP as long as the load calculations are under 1,000 amps.

Thanks
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
I think the point he was trying to make is that when you have a circuit that is a designed for a specific fixed load you really do not need (outside of rules) overload protection. All you would need for safety is short circuit protection. This of course assumes the load can not increase.

It is worth noting that the nec already uses this type of concept when it comes to service conductors supplying more than one service disconnecting means. For example if you use the exception you can have 1,000 amps of wire 'protected' by 3,000 amps of OCP as long as the load calculations are under 1,000 amps.

Exactly my point. If you have a fixed load there is no way to add more load to that circuit unlike multiple receptacles so in theory you do not need overload protection, just short circuit and ground fault protection.

Only reason for the breaker size increase by 125% is to take into account continuous loading (panel board heat build up).
 

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Is there anything inherently wrong with treating these small conductors this way?


Unless someone (unqualified) adds more baseboards, nothing.


Is it dangerous?

IMO no, the conductor do not see loading over those in table 310.15 (B) (16)


Is it costly?

Saves on a lot of copper and labor, hence why considering making this a code proposal.


Does it save more than it costs?


Yes.


What do you think?
 
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