# Contactor load wires burning up



## Galt (Sep 11, 2013)

Poor connection or bad contacts.


----------



## telsa (May 22, 2015)

Not knowing the full picture... do keep in mind that Constant Wattage Transformers REALLY suck down the Watts until the lumiere really comes up to power. 

*If* this technology is in use -- then your conductors are routinely seeing surges way past 40A every time the lamps fire up.

HO fluorescents also draw heavily -- but they are better behaved. But you're right up against conductor limits.

Every EE designed lighting scheme I've ever touched limits the FLA of the circuit to 55-60% of the NEC continuous load limit: 10A for #12 at 277 VAC L-N -- 15A for #10 at 277 VAC L-N.

Who designed this stressed scheme ?


----------



## gpop (May 14, 2018)

25 amps is at the higher limit of a ring terminal so there's less room for weak connection. Buy a quality crimper and dont re-use the contactors just replace them.


----------



## dronai (Apr 11, 2011)

Was going to suggest high temp ring terminals, but you already tried them.


----------



## CoolWill (Jan 5, 2019)

Only half of the contactor poles are being used.... Barring a rewire with larger wire or higher amp contractors, I might utilize both poles in parallel to take the stress off.


----------



## telsa (May 22, 2015)

I'm thinking that your Power Factor is anything but 100%.

The scheme needs a re-wire.

Your conductors can handle FLA at such power levels only IF the PF is 100%.

100% PF is what you see in incandescent lamps... and only incandescent lamps.

At 80% PF you're drawing 31.25 Amps -- Reactively.

31.25A X .80 = 25A

Just what is the PF for those lights ?

You can see why EEs de-rate lighting conductors so severely.


----------



## tates1882 (Sep 3, 2010)

I would pull a few more switch legs.


----------



## FishinElectrcian (Jul 18, 2019)

Yeah those look like a definite purpose 30A contactor with 24V coil? I see them all the time in the Monitron boilers.. They really aren't very good to push 30A through, for starters they are somewhat open and prone to dust. I've actually had better luck with the wide open ones or a better grade of sealed contactor. Oddly enough from the factory if those are the same ones, Monitron loads them past 30A from the factory... they are rated resistive usually and your inductive load is probably too much. No I don't know why that's worse than resistive. F###n Google it. Peace out.


----------



## gpop (May 14, 2018)

CoolWill said:


> Only half of the contactor poles are being used.... Barring a rewire with larger wire or higher amp contractors, I might utilize both poles in parallel to take the stress off.


Yep was thinking the same thing. Use both side then add nickel plated tool wire jumpers and wirenut that back to the original. It wont fix a bad design but it will move the problem further down the chain.


----------



## splatz (May 23, 2015)

The cost of the rewire is going to pay for those LEDs, then the LEDs are going to pay for themselves with the lower utility bill, then pay you again when you don't have to replace lamps every so often, then whack you again when the fixtures have to be replaced in ten years. This is the circle of life.


----------



## micromind (Aug 11, 2007)

I don't think it's the contactor, I think it's the crimp connectors. I never use that type of connector over 10 amps, seen too many burn up at high currents. 

With contactors that have only screws, I use some sort of setscrew lug under the screws, copper is best. Or get contactors that have box lugs. 

Also, I never load that type of contactor to more than half its rating.


----------



## Bird dog (Oct 27, 2015)

How often do the motion sensors turn the lights on & off? The wire/connection may not be given a chance to cool off. The wire acts like a heatsink for the connection just like the wire acts like a heat sink for the breaker maybe.


----------



## oliquir (Jan 13, 2011)

bad crimp tool will do that, i have a place where the only way to make them last were crimping + solder


----------



## paulengr (Oct 8, 2017)

I thought DP contactor stands for Don’t Purchase?

DP contactors are rated for 1.0 power factor loads only...as in Edison lights. You CAN derate them but it’s so painful IEC is actually easier.

It also sounds like maybe you are getting voltage drop especially at that much current. If you do then it raises your current even higher because LED drivers are current regulators and not voltage...low voltage makes them crank up the power. The wiring resistance eats up extra power. An ohm per foot matters when you have a lot of feet or a big load. On long LED strings over sizing conductors or lots of home runs based on voltage drop is very important.


----------



## JRaef (Mar 23, 2009)

Actually, it looks to me as though that is #8 high strand count (Class G) extra flexible wire. You cannot use standard Stakon crimps for that, it requires not only specially rated lugs, it requires a special crimp die as well. If you use standard crimps, the connection can be too "soft" and results in high resistance. What you are showing in those photos is *exactly *what happens.


----------



## JRaef (Mar 23, 2009)

Corroborating evidence:
https://lugsdirect.com/GuideToFlexFlexibleFineStrandedWireCableMechanicalLugsFAQ.html


----------



## CMP (Oct 30, 2019)

*Overheated Contactors*



Robbie Rob said:


> Having trouble understanding why wires are burning up in this control cabinet.
> The control cabinet works 8 tennis courts each court has a motion sensor that turns on a contactor that controls 10 fixtures. * The load side of the contactor is where the problem is.* The wires are burning up after the contactor at the stake on terminals. *Each circuit is pulling 24–25A on a 30 amp breaker at 277 V it’s on number 10 stranded wire with a steak on crimped. The breakers never trip. *
> The wires are not derated properly going back to the fixtures in the conduit but I don’t think that should have any effect on the wire at the Contactor.
> 
> If anyone has any advice I would greatly appreciate it thank you.



My take on the issue is that the lighting control panel was field wired for half as many circuits as it was designed for. The field installer decided to use 30A fully loaded circuits, instead of the normal 20A lighting circuits, and ignored the rating of the panel component's.


You have 8 zones, and 16, 2 pole contactors. If it was supplied and wired with 32, 20A 277V circuits, you would not have this problem.


The contactors are likely rated for 20A inductive load, and their placed under a 25A inductive load. No amount of termination alteration is going to prevent them from overheating, and transferring that heating to the wiring.


Here is some data from a similar definite purpose contactor.



























If you look closely at the prior damage, you can see that the contactor screw terminals, fixed contact blade and the movable contacts are heat damaged and oxidized even before the crimp terminals are burned off the wiring. It's not happening just on the load side of the contactors. The load side overheats more because it has twice the contact resistance of the line side termination.




















Its getting hot enough to oxidize the zinc plating on the screw heads and oxidize the contactor parts. No copper terminal, wire or connector is going to stand up to that kind of heat over the long term.


For long lasting results the job needs to be rewired with twice the number of 20A circuits, the contactors upgraded to ones suitable for the load, or the load reduced. No free lunch here.


Converting it into a big box of wirenut splices is not going to help either. Take it for what its worth. I would explain the problem to the owner and let them decide how to proceed, instead of applying bandaids to the problem.


----------



## Robbie Rob (May 14, 2017)

Each fixture has (4) 4 lamp ballast. There is one circuit for main lighting which feeds three of the four ballasts. Which is pulling 25 A. There is another circuit that is for auxiliary lighting that controls the last ballast. They never turn on this extra circuit to save money on electric. And they do not need extra light. 
I was thinking if I rewire the fixtures and make one circuit control two ballasts and one circuit control one ballast. I can drop the load down by 1/3 on the overloaded circuit. 
I’m just concerned if I do this I don’t want it to still be a problem. I want to make sure it will solve it before I do all that work. it should be around 16.6 A once the third ballast is switched to another circuit. I would also remove all the crimp terminals.


----------



## CMP (Oct 30, 2019)

It would be best to stop approximating, and check the labels on the ballasts and contactors, to engineer a proper fix. You know what you have don't last. Others have mentioned that power factor matters, as well as the actual VA ratings of the ballasts.


Same for the contactors, were not sure of the ratings, of what exists now, that we know don't last. Looks to me you have some ABB DP20C3P-1 rated at 20A inductive. As mentioned by others your actual load with the power factor of .8 applied is likely higher than 31A continuous load.


For a 20A inductive rated contactactor I wouldn't be loading that at more than 16A tops. So I don't like the idea of a 16.6A load either. It's too close for comfort. Your wire is also running warm, and you don't want the contacts adding more heat to them.


Without any component data, my guess at a solution would be to replace the overloaded contactors with a 40A inductive model, and leave the load as connected.


A 40A rated model would be above your loading point, contribute much less contact resistance and heat. It is also available in a box lug connection, so it could eliminate the stake-on connection. With some brands a pressure plate connection is also available.


And the 40A models have the same footprint as your existing 20A units. With a box lug model, your conductor can land directly on the fixed contact blade, and have more thermal mass as compared to a stake-on terminal.


As to the burnt conductors, taping up some oxidized copper conductor is never a good solution, whatever way it's connected. It should be cut back to past the damaged area, and replaced with a fresh piece. I would be using some un-insulated butt splices and shrink tube to get the best crimp connection. Avoid the use of wire nuts in a control panel that is already stuffed.



Best to check your ballasts and contactor ratings first though.


ABB Definite Purpose Contactors PDF


DP40C2P-1 40A Inductive


----------



## VELOCI3 (Aug 15, 2019)

Instead of sta-cons or wrapping #10 solid around the terminal screws put mechanical lugs in. Put some no corrode or penetrox on the wire too. Obviously the connection is failing. Also the internal contact surfaces are probably pitted. Replace the whole relay. 


Sent from my iPhone using Tapatalk


----------



## just the cowboy (Sep 4, 2013)

If you are even thinking of changing the loads make sure they are not sharing a neutral and if you rearrange the circuits it may overload the neutral.


----------



## dronai (Apr 11, 2011)

VELOCI3 said:


> Instead of sta-cons or wrapping #10 solid around the terminal screws *put mechanical lugs in*. Put some no corrode or penetrox on the wire too. Obviously the connection is failing. Also the internal contact surfaces are probably pitted. Replace the whole relay.
> 
> 
> Sent from my iPhone using Tapatalk


Lugs are a good idea, if they can fit in that area


----------

