Message Board Thread - "Relay coil temperature normal or not??"

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Relay coil temperature normal or not?? i2r 3/10/2005
During a survey electrical cabinets we see a lot of high relay coil temperatures. Temperatures occur over the 100ºC with "normal relays" 24V DC or AC. When you look at the specs of the distributor you only get inforamtion about max. Tambient. We have one report which tells us that the temperature of the coil in air according EN 60947-5-1 should be < 100ºC with an insultion E type. Can someone tell me more about the maximum allowable temperature for these components and what makes it this high? Coulsd it be the suply voltage, or the distortion of the voltage/current?
Re:Relay coil temperature normal or not?? Manuel 3/12/2005

i had seen this type of high temperature relays.
if this relays are 24 volts definitive there is a problem, maybe aging (coil insulation degradation), voltage diferent from relay uses (sometimes ac instead dc), overvoltage or undervoltage, huge current thru relay contact's or contact's surface flamed. long, long periods at ON state.

inspect carefully the protective relay box, over 100 C must be starting to show physical damage.

24 volts relays are really cheaper, try new one and see what happens.

good luck
Re:Relay coil temperature normal or not?? electricpete 3/14/2005
Insulation type would be a key determining factor in determining max temperature as you mentioned.

Some general comments:
- Hi voltage can cause overheating.
- Low voltage can cause overheating (!). A electromagnetic plunger type relay or contactor which remains energized at lower voltage after it has "dropped out" will draw excessive current and overheat due to change in the magnetic circuit. To avoid this, normally there should be some contacts that will completely deenergize the relay after it drops out.
- A 24vac relay used in a 24vdc system will definitely overheat.
- Harmonics you mention are a possibility.
- Aging might cause relay to run hotter. Degradation of interlaminar core insulation in particular. Less likely degradation or electrical turn-to-turn insulation... would normally lead to a failure pretty quickly.
- >100C might be normal?

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