Marley Heater Fire Hazard?

[wire nut]

Folks,
Recently I installed several Marley ?K? Series Fan Forced Wall Heaters. Each heater runs on 220 vac SINGLE PHASE and is rated a 4000 watts each. I wired the rooms with #10 from each heater to the panel. The heaters draw ~16 amps on each leg as measured with my amp probe. While installing the heaters, I noticed that the internal wiring used in each heater was #14 wire which is really pushing the limits.

Today, I was reading the Installation and Maintenance Instructions as published by Marley. In the documentation, it listed the use of #14 wire for the ?power supply cable? to the heater for it?s 3 phase model. No mention about it?s single phase model that I installed. The heaters I installed are single phase and can?t be converted to 3 phase.

My questions: Is there a fire hazard within these units since #14 wire is used and these heaters will draw about 16 amps continuous on each leg when activated? Is there a design flaw? I did not see any recalls for these units or reports of fires. If memory serves me correctly, they used #14 wire rated at 105 degrees C.

John
New Jersey

 

[hbiss]

Re: Marley Heater Fire Hazard?

The manufacturer can use anything they want to wire their product internally as long as the get their listing. What you do is another matter.

[ November 13, 2003, 02:03 PM: Message edited by: hbiss ]

 

[hbiss]

Re: Marley Heater Fire Hazard?

The manufacturer can use anything they want to wire their product internally as long as the get their listing. What you do is another matter. Their 3 phase unit will draw less current per phase than a single phase heater of a given wattage so 14 ga might be appropriate there.

 

[wire nut]

Re: Marley Heater Fire Hazard?

hbliss,
You missed my point. The heaters I wired are SINGLE PHASE rated at 4000 watts, pulling about 16 amps continuous per leg. The internal wiring in the unit uses #14.

I am fully aware of 3 phase and the usuage IF the heater was 3 phase.

Why would a manufacture use #14 wire knowing the unit will draw amperage above the wire's rating???? I see this as a fire hazard.

As far as a manufacture could use anything they want is bull. Honeywell had a recall on a particular electric thermostat model due to potential fire hazard.

John
New Jersey

 

[don_resqcapt19]

Re: Marley Heater Fire Hazard?

John,
The ampacity of 60?C #14 is 20 amps so there is no real problem running a 16 amp load on the internal #14s. See Table 310.16.
Don

 

[tonyi]

Re: Marley Heater Fire Hazard?

Its not the wire's rating per se, rather the insulation temp rating.

A #14 MTW(105C) could handle 16A and have the insulations be well under a 105C operational max. This isn't acceptable for an ordinary building wire applications, but within an engineered unit it could work OK where all the internal terminations are designed to operate at the higher temps.

 

[wire nut]

Re: Marley Heater Fire Hazard?

Don and TonyI, thanks for the explaination. I guess I got a bit worried to see #14 used in the Marley unit and reading about a recall on a particular model Honeywell thermostat that was somewhat under rated causing a fire hazard. Personally, Ii hate when equipment is engineered to minimum standards to save a penny or two and I still don't like the idea of #14 subjected to a continuous 16 amps regardless of the 105 degree C rating.

John
New Jersey

 

[don_resqcapt19]

Re: Marley Heater Fire Hazard?

Tony,
The 105?C rating is not needed for this application. The temperature of the #14 will not exceed 60?C with a 20 amp load.
Don

 

[tony_psuee]

Re: Marley Heater Fire Hazard?

One further comment on what the manufacturer used for wiring. Wirenut, you are correct that they can not use anything they want if it is a listed product. UL has different ampacity ratings for conductors based on the fact that they are open air. Although most of them closely follow Table 300.17. Having worked for an OEM with a UL 508A panel shop we used conductors that would be undersized per NEC, but were in full compliance with UL requirements. IMO the key on any product is that it is listed by an approved agency, UL, ETL, etc, and not the marketing BS that it is designed to the requirements. Designing to and getting it listed are two different things.

Tony

 

[hbiss]

Re: Marley Heater Fire Hazard?

By "they can use anything they want" I was saying the they have other options in wiring material than we do. If their choice were not proper they would not get their listing.

 

[bennie]

Re: Marley Heater Fire Hazard?

Remember that conductors, on heating equipment, are subjected to heat from the current flow plus the ambient temperature. The insulation is heated from within and without.

The ampacity of 60?C insulated wire is zero at 140?F. 90?C insulated wire is zero at 194?F.

 

[hillbilly]

Re: Marley Heater Fire Hazard?

Hey bennie, haven't heard from you in a while. Would you please expound on your last statement about wire ampacity and temperature.
thanks
steve