[lynes.nathan]

Is a electric heater with a fan motor in it to blow the heat still covered under section 62? Reading 62-000 I think it is still covered but other posts I have read on this forum say it is not covered. They say if its not 100% resistive load then its not covered by that section. Just wanted to clarify.

 

[Vintage Sounds]

Yes, why wouldn't it be? You are thinking of a specific rule covering overcurrent protection for fixed resistance heating loads - 62-114(7)

(7) Service, feeder, or branch conductors supplying only fixed resistance heating loads shall be permitted to have an ampacity less than the rating or setting of the circuit overcurrent protection, provided that their
ampacity is
(a) not less than the load; and
(b) at least 80% of the rating or setting of the circuit overcurrent protection.

 

[lynes.nathan]

Yes, why wouldn't it be? You are thinking of a specific rule covering overcurrent protection for fixed resistance heating loads - 62-114(7)

So a heater with a fan motor is not considered a fixed resistance heating load?


What im really trying to figure out is if I have a heater with a fan motor can I follow the rule:

(7) Service, feeder, or branch conductors supplying only fixed resistance heating loads shall be permitted to have an ampacity less than the rating or setting of the circuit overcurrent protection, provided that their
ampacity is
(a) not less than the load; and
(b) at least 80% of the rating or setting of the circuit overcurrent protection.

 

[lynes.nathan]

So a heater with a fan motor is not considered a fixed resistance heating load?


What im really trying to figure out is if I have a heater with a fan motor can I follow the rule:

(7) Service, feeder, or branch conductors supplying only fixed resistance heating loads shall be permitted to have an ampacity less than the rating or setting of the circuit overcurrent protection, provided that their
ampacity is
(a) not less than the load; and
(b) at least 80% of the rating or setting of the circuit overcurrent protection.

Re-reading this I don't think a heater with a fan motor counts because it is not a fixed resistance heating load. So this rule does not apply.

 

[FrunkSlammer]

I think it fits, but what do I know.

What I'm curious about i how big of a heater are you installing that you want/need to undersize the conductors?

 

[lynes.nathan]

I think it fits, but what do I know.

What I'm curious about i how big of a heater are you installing that you want/need to undersize the conductors?

Its a three phase 7500 watt 208 volt forced fan heater. #12 AWG got pulled before the heater was changed to 208 volts. Before it was 600 volts. Here is what I come up with:

Amps = 7500 / (1.73 X 208)

Amps = 20.8


Now sizing the circuit breaker:

Rule 62-144(6)(b)

20.8 x 1.25
= 26

Rule 62-114(8) (From the Pocket Reference code book)

if no match exists, round up to the next higher standard rated circuit breaker or fusible switch

Based on that I go with a 30 amp breaker.


Now conductor size:

Rule 62-114(7)(b) (From the Pocket Reference code book)
When using larger than the minimum standard rated circuit breaker or fusible switch: the ampacity of the standard rated overcurrent device x 0.8


So based upon that 30 x 0.8 = 24. Looking at table 2 75 degree column I can used # 12 AWG. Or do I have to go to #10 AWG because it is not a fixed resistance heating load.

 

[Tsmil]

Its a three phase 7500 watt 208 volt forced fan heater. #12 AWG got pulled before the heater was changed to 208 volts. Before it was 600 volts. Here is what I come up with: Amps = 7500 / (1.73 X 208) Amps = 20.8 Now sizing the circuit breaker: Rule 62-144(6)(b) 20.8 x 1.25 = 26 Rule 62-114(8) (From the Pocket Reference code book) if no match exists, round up to the next higher standard rated circuit breaker or fusible switch Based on that I go with a 30 amp breaker. Now conductor size: Rule 62-114(7)(b) (From the Pocket Reference code book) When using larger than the minimum standard rated circuit breaker or fusible switch: the ampacity of the standard rated overcurrent device x 0.8 So based upon that 30 x 0.8 = 24. Looking at table 2 75 degree column I can used # 12 AWG. Or do I have to go to #10 AWG because it is not a fixed resistance heating load.

I believe you have to go with the 10s. Your limited to 20 amp breaker for the 12s.

 

[corisu]

14-104 (1c), 14-104 (2) makes this rule void when dealing with section 62. Based off your calc you're fine with #12's on the 30a breaker. You meet the 80% ampacity rating 62-114 (7b)

 

[Tsmil]

14-104 (1c), 14-104 (2) makes this rule void when dealing with section 62. Based off your calc you're fine with #12's on the 30a breaker. You meet the 80% ampacity rating 62-114 (7b)

Problem being that fan. Fixed resistive heating loads only. Fan messes things up. Check with your inspector, mine wouldn't allow it.

 

[corisu]

Im curious how your inspector would size conductors/ocp for boilers and furnaces?

 

[Wpgshocker]

If it isn't a fixed resistive load, why are you trying to make the code rule work?
You have to rewire it, just do it right and avoid the hassles.

 

[corisu]

Is a fixed resistive load a load with an ohmic value that cannot be adjusted? If so then his heater falls into that category. All heat is wire to the load bump the breaker.

 

[Wpgshocker]

Is a fixed resistive load a load with an ohmic value that cannot be adjusted? If so then his heater falls into that category. All heat is wire to the load bump the breaker.

You wire it according to manufacturer spec.

 

[Vintage Sounds]

The fan motor is an inductive load. As soon as that becomes part of the mix the total load is no longer purely resistive so you still have to comply with 14-104(2)

(2) Except as provided for by Subrule (1)(c), the rating of overcurrent protection shall not exceed
(a) 15 A for No. 14 AWG copper conductors;
(b) 20 A for No. 12 AWG copper conductors;
(c) 30 A for No. 10 AWG copper conductors; and
(d) 15 A for No. 12 AWG aluminum conductors.

 

[corisu]

So inductive loads comply with 14-102?

 

[corisu]

Typo 14-104.

 

[Vintage Sounds]

Well since 14-104 basically applies to everything except when otherwise specified, I'm going with yes since fan heaters don't have a special rule that applies only to them.

 

[lynes.nathan]

The fan motor is an inductive load. As soon as that becomes part of the mix the total load is no longer purely resistive so you still have to comply with 14-104(2)

(2) Except as provided for by Subrule (1)(c), the rating of overcurrent protection shall not exceed
(a) 15 A for No. 14 AWG copper conductors;
(b) 20 A for No. 12 AWG copper conductors;
(c) 30 A for No. 10 AWG copper conductors; and
(d) 15 A for No. 12 AWG aluminum conductors.



Agreed! #10 AWG it is!

 

[corisu]

62-108 (1B) branch circuit consuctors shall have an ampacity not less than that of the load supplied
62-108 (C) for the purpose of this rule an approved unit that that combines heating with ventillation or lighting equipememt, or both shall be considered to be heating equipment.

 

[corisu]

Unit heater falls under the category of fixed resistance heating load. Example of variable resistance heating load would be self regulating heat trace