Heaters

[George Rivers]

The built-in fuses used to prevent overload in specialized systems are called "Heaters". Is the term "Heaters" a general term or do they have a specific name? If so why are they called "Heaters"?

 

[iwire]

Re: Heaters

I think you are talking about motor starter heaters?

Typically a motor starter is made up of a switch (manual or contactor) and an overload unit.

The overload unit has switches in it that are operated by heat.

In order to precisely protect a motor you select a set of 'heaters' that are designed to operate the switches in the overload unit when a predetermined amount of current flows through them.

Do not call them fuses as they have little if any similarities to fuses.

They do not protect against short circuits only overload conditions.

 

[kiloamp7]

Re: Heaters

Yes, "heaters" is a general term & I've even heard the slang terms "bimetals" and "solderpots" used.

But Square D calls them "overload relay thermal units" .

 

[jwelectric]

Re: Heaters

430.6(A) (2) Nameplate Values. Separate motor overload protection shall be based on the motor nameplate current rating.
III. Motor and Branch-Circuit Overload Protection
430.31 General.
Part III specifies overload devices intended to protect motors, motor-control apparatus, and motor branch-circuit conductors against excessive heating due to motor overloads and failure to start.
Overload in electrical apparatus is an operating overcurrent that, when it persists for a sufficient length of time, would cause damage or dangerous overheating of the apparatus. It does not include short circuits or ground faults.
100 Overload. Operation of equipment in excess of normal, full-load rating, or of a conductor in excess of rated ampacity that, when it persists for a sufficient length of time, would cause damage or dangerous overheating. A fault, such as a short circuit or ground fault, is not an overload.

Although I have them called ?heaters? and in past time called them ?heaters? myself the NEC refers to them as overload devices.

 

[iwire]

Re: Heaters

Originally posted by jwelectric:
Although I have them called ?heaters? and in past time called them ?heaters? myself the NEC refers to them as overload devices.

Mike I have to disagree.

Overload devices take many forms, sometimes the overload device is just a fuse. Some overload units are full electronic and do not have heaters at all.

'Heaters' are not themselves overload devices they must be installed in an overload device.

Think of it this way, could I use the heaters by themselves and satisfy 430.6(A)(2).

As kiloamp7 pointed out 'overload relay thermal units'.