# 80% Loading of Circuits for Continuous Loads



## 1.21gigawatts (Jun 22, 2013)

brodgers said:


> Have a job where I am adding a low voltage thermostat to existing fan-forced electric wall heaters recessed into the wall. Normally this is a no brainer with a relay and a transformer. There are 6 heaters with a nameplate rating of 3000 watts at 240 volts. The heaters are split between 3 circuits with 2 heaters on a circuit.
> 
> Does the 80% circuit loading for continuous loads rule apply to only the OCPD or does it also apply to the switching equipment? Normally I use Honeywell R841 electric heat relays and would use 3 R841D1036 relays on this job (1 for each circuit). The rating on the relay is stamped 25 amps @ 240 volts (6000 watts). If I use 1 relay per circuit then the relays would be controlling a continuous load that is 100% of their rating. Is this to code or do I need to separate the heaters all onto their own relays?



Yes, you ill need to provide OCPD at 125% of KW rating because its a continious load. This applies to control as well. Its all in nec 424


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## Black Dog (Oct 16, 2011)

III. Control and Protection of Fixed Electric Space-Heating Equipment
424.19 Disconnecting Means. Means shall be provided to simultaneously disconnect the heater, motor controller(s), and supplementary overcurrent protective device(s) of all fixed electric space-heating equipment from all ungrounded conductors. Where heating equipment is supplied by more than one source, feeder, or branch circuit, the disconnecting means shall be grouped and marked. The disconnecting means specified in 424.19(A) and (B) shall have an ampere rating not less than 125 percent of the total load of the motors and the heaters and shall be lockable in accordance with 110.25.
(A) Heating Equipment with Supplementary Overcurrent Protection. The disconnecting means for fixed electric space-heating equipment with supplementary overcurrent protection shall be within sight from the supplementary overcurrent protective device(s), on the supply side of these devices, if fuses, and, in addition, shall comply with either 424.19(A)(1) or (A)(2).
(1) Heater Containing No Motor Rated over 1⁄8 Horsepower. The disconnecting means specified in 424.19 or unit switches complying with 424.19(C) shall be permitted to serve as the required disconnecting means for both the motor controller(s) and heater under either of the following conditions:
(1) 
The disconnecting means provided is also within sight from the motor controller(s) and the heater.
(2) 
The disconnecting means is lockable in accordance with 110.25.
(2) Heater Containing a Motor(s) Rated over 1⁄8 Horsepower. The above disconnecting means shall be permitted to serve as the required disconnecting means for both the motor controller(s) and heater under either of the following conditions:
(1) 
Where the disconnecting means is in sight from the motor controller(s) and the heater and complies with Part IX of Article 430.
(2) 
Where a motor(s) of more than 1⁄8 hp and the heater are provided with a single unit switch that complies with 422.34(A), (B), (C), or (D), the disconnecting means shall be permitted to be out of sight from the motor controller.
(B) Heating Equipment Without Supplementary Overcurrent Protection.
(1) Without Motor or with Motor Not over 1⁄8 Horsepower. For fixed electric space-heating equipment without a motor rated over 1⁄8 hp, the branch-circuit switch or circuit breaker shall be permitted to serve as the disconnecting means where the switch or circuit breaker is within sight from the heater or is lockable in accordance with 110.25.
(2) Over 1⁄8 Horsepower. For motor-driven electric space-heating equipment with a motor rated over 1⁄8 hp, a disconnecting means shall be located within sight from the motor controller or shall be permitted to comply with the requirements in 424.19(A)(2).
(C) Unit Switch(es) as Disconnecting Means. A unit switch(es) with a marked “off” position that is part of a fixed heater and disconnects all ungrounded conductors shall be permitted as the disconnecting means required by this article where other means for disconnection are provided in the types of occupancies in 424.19(C)(1) through (C)(4).
(1) Multifamily Dwellings. In multifamily dwellings, the other disconnecting means shall be within the dwelling unit, or on the same floor as the dwelling unit in which the fixed heater is installed, and shall also be permitted to control lamps and appliances.
(2) Two-Family Dwellings. In two-family dwellings, the other disconnecting means shall be permitted either inside or outside of the dwelling unit in which the fixed heater is installed. In this case, an individual switch or circuit breaker for the dwelling unit shall be permitted and shall also be permitted to control lamps and appliances.
(3) One-Family Dwellings. In one-family dwellings, the service disconnecting means shall be permitted to be the other disconnecting means.
(4) Other Occupancies. In other occupancies, the branch-circuit switch or circuit breaker, where readily accessible for servicing of the fixed heater, shall be permitted as the other disconnecting means.


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## Carultch (May 14, 2013)

brodgers said:


> Have a job where I am adding a low voltage thermostat to existing fan-forced electric wall heaters recessed into the wall. Normally this is a no brainer with a relay and a transformer. There are 6 heaters with a nameplate rating of 3000 watts at 240 volts. The heaters are split between 3 circuits with 2 heaters on a circuit.
> 
> Does the 80% circuit loading for continuous loads rule apply to only the OCPD or does it also apply to the switching equipment? Normally I use Honeywell R841 electric heat relays and would use 3 R841D1036 relays on this job (1 for each circuit). The rating on the relay is stamped 25 amps @ 240 volts (6000 watts). If I use 1 relay per circuit then the relays would be controlling a continuous load that is 100% of their rating. Is this to code or do I need to separate the heaters all onto their own relays?


Unless the manufacturer's documentation indicates otherwise, any OCPD or disconnecting device (or a device that does both) requires the 1.25 factor for continuous loads. To see if the manufacturer's documentation says otherwise, look for terms such as continuous duty rated, rated for continuous duty, fully rated, or 100% rated.

A continuous load is defined as a load where the maximum current is expected to continue for 3 hours or more.

Most overcurrent devices will not be continuous duty rated, and thus require the 1.25 factor. This is the case for both fuses and breakers. Continuous duty rated breakers are rare, continuous duty fuses are even more rare.

It is common for switching devices that do not include an integrated OCPD, to be rated for continuous duty. A couple examples are your standard unfused safety switch, and rotary switches. Relays and contactors are much more interesting, and you may have to confirm your application with the manufacturer.

In any case, you do have to check documentation if you would like to take advantage of a continuous duty rating.


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## brodgers (Aug 5, 2007)

Thank you for the responses!

I will have to dig into this further with Honeywell. There is a discrepancy between the rating stamped on the relay versus what is published in the spec sheets. I have emailed Honeywell's customer support to get clarification and am waiting for a response. The relay is stamped with a higher rating that what is published in their catalogs and spec sheets.


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## oliquir (Jan 13, 2011)

ocpd needs 125% but not the thermostat or relays, but i wouldn't put 25 amps load on a 25amp relay, i would use a 40amp relay minimum for 25 amps load but that is not required
on honeywell page they are only recommended for up to 5000W loads


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## brodgers (Aug 5, 2007)

oliquir said:


> ocpd needs 125% but not the thermostat or relays, but i wouldn't put 25 amps load on a 25amp relay, i would use a 40amp relay minimum for 25 amps load but that is not required
> on honeywell page they are only recommended for up to 5000W loads


There's a discrepancy with what the Honeywell page shows and what is stamped on the relay itself. Relay is stamped for 6000 watts load. Regardless I was leaning towards putting each heater on a separate relay which seems to be the consensus. I can put most of the relays near the panel and run the low voltage in Wiremold from the thermostat to the panel room.

The construction of the addition with these heaters is block and plaster. It was wired with conduit so I can pull additional wires to some of the heaters. Unfortunately I will be limited to what I can pull before I have to start derating. I am considering getting creative and mounting a relay with a small transformer in one of the wiring compartments of a heater to control the heater downstream that I cannot easily run wire to. The heaters are recessed into the block so running new conduit or wiremold for the line voltage is out of the question.


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