lighting contactor

[rippledipple]

Hi,I want to install a fuse block to protect both sides of contactor coils which keep burning up in power outages that happen quit often at a condo complex.Each building has a cabinet with 3 or 4 small 20a 3pole lighting contactors in them. The coils are very small and i believe it takes about 1 amp to close. so do i try an 1.5 amp or 2 amp fuse???? I don't want it to be a nuisance to maintenance man. Any help would be appreciated!!!

 

[Smart $]

Coils should not burn up from power outages. There may be surge problems which are burning out the coils... but not outages. You can try fusing, but I have to wonder if that will eliminate the problem.

You need to determine exactly what the pull-in current is before determining fuse size.

 

[rippledipple]

coil

coil

Coils should not burn up from power outages. There may be surge problems which are burning out the coils... but not outages. You can try fusing, but I have to wonder if that will eliminate the problem.

You need to determine exactly what the pull-in current is before determining fuse size.

I believe it is when the power comes back on is what is burning them out.

 

[iwire]

Coils should not burn up from power outages.

I find it pretty common when only one ungrounded line is dead.

I assume it is because they end up with a under voltage backfeed of sorts through other equipment.

 

[luckylerado]

I believe it is when the power comes back on is what is burning them out.

How is that different then energizing the coil with a photocell or HAO?

Is the neutral part of a MWBC or the control circuit share a lighting circuit?
Have you considered a mechanically held contactor?

 

[iwire]

Have you considered a mechanically held contactor?

:thumbsup:

 

[mgookin]

If you keep running to the supply house to get the same part #, I wonder if someone at one time installed the wrong part # because that's what was on the truck.

 

[Ingenieur]

They make surge protectors/suppressors that go across the coil

 

[rippledipple]

coil

coil

They make surge protectors/suppressors that go across the coil

That may work,I'll check into that, thx

 

[rippledipple]

coil

coil

That may work,I'll check into that, thx

the mech held coil also,but can i get that part for my existing contractors????

 

[Ingenieur]

the mech held coil also,but can i get that part for my existing contractors????

for a mech latching contactor control wiring will need revised

 

[Smart $]

I find it pretty common when only one ungrounded line is dead.

I assume it is because they end up with a under voltage backfeed of sorts through other equipment.

I suppose that could happen on a 208Y/120 supplied condo. I was thinking 120/240 where the power outage wasn't because of the local transformer.

 

[GoldDigger]

How is that different then energizing the coil with a photocell or HAO?

Is the neutral part of a MWBC or the control circuit share a lighting circuit?
Have you considered a mechanically held contactor?

A typical contactor's AC coil will draw more current when energized in the open position than it will once the armature has moved and the magnetic circuit is complete.
I can see a reduced voltage that is just below what is required to pull in the contacts generating enough heat to burn out the coil if it stays at that voltage for a long time.
Or, as was mentioned, a compromised neutral can cause almost anything to burn out.

 

[big john]

Interesting: On large contactors it works the other way around: High voltage to overcome the air gap and pull the armature, but once actuated the economizer circuit kicks in and reduces the holding voltage so the coil doesn't overheat.

 

[kwired]

Interesting: On large contactors it works the other way around: High voltage to overcome the air gap and pull the armature, but once actuated the economizer circuit kicks in and reduces the holding voltage so the coil doesn't overheat.

Kind of works that way on smaller contactors, you need more voltage to pull them in then you do to hold them in, they usually don't have any method of reducing voltage after pulled in though.

 

[kwired]

A typical contactor's AC coil will draw more current when energized in the open position than it will once the armature has moved and the magnetic circuit is complete.
I can see a reduced voltage that is just below what is required to pull in the contacts generating enough heat to burn out the coil if it stays at that voltage for a long time.
Or, as was mentioned, a compromised neutral can cause almost anything to burn out.

My bet is on this being OP's troubles. Perhaps OP needs undervoltage relay wired into the control circuit so the contactor coils are isolated when there is not full voltage.

Fuses as initially suggested might protect the coils, but will still be left with equipment not working just as frequently because of blown fuses. Find the problem, don't just treat the symptoms.

 

[Smart $]

Interesting: On large contactors it works the other way around: High voltage to overcome the air gap and pull the armature, but once actuated the economizer circuit kicks in and reduces the holding voltage so the coil doesn't overheat.

High currrent, i.e. inrush. What economizer circuit? Just how large a contactor are you talking?

Overheating occurs from not enough EMF to pull in armature because of insufficient current, a likely result of undervoltage.

 

[Ingenieur]

Pg 6 representative values http://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/vol05_tab04.pdf
pick up 30-40 va
sealed 6-8 va
sealed 2-3 watt

obviously depends on size

 

[GoldDigger]

Interesting: On large contactors it works the other way around: High voltage to overcome the air gap and pull the armature, but once actuated the economizer circuit kicks in and reduces the holding voltage so the coil doesn't overheat.

It actually works the same way around.
Once the contacts pull in the current is reduced because of the increased inductance.
But the required holding force is reduced even more. That allows you, if you wish, to reduce the voltage and drop the current even more.
If you have a DC coil the automatic reduction will not happen, making it more likely that the manufacturer will provide a circuit to reduce the voltage. There is more control power to be saved in a larger contactor.

 

[big john]

High currrent, i.e. inrush. What economizer circuit? Just how large a contactor are you talking?

Overheating occurs from not enough EMF to pull in armature because of insufficient current, a likely result of undervoltage.

I'm thinking MV contractors. Different issue from inrush: They often have a separate control circuit that reduces coil voltage and current after seal-in.