get your clever hats out

[petersonra]

I have an interesting problem. A project I am working on has 100 contactors with one contact jumped together. We used solid wire for this jumper, but there are 200 connections, and there is a noticable voltage drop from one end of the chain to the other. Normally I would not much care, but it actually matters this time.

I am trying to come up with a relatively cheap solution. Some kind of custom jumper bar maybe?

if it was just one of them I would just have them put in bigger jumpers, but there are 14 of these beasts we are retrofitting.

 

[mivey]

Pigtails .

 

[Cold Fusion]

I have an interesting problem. A project I am working on has 100 contactors with one contact jumped together. ...

...there are 200 connections, and there is a noticable voltage drop from one end of the chain to the other. ....

Possibly these 100 auxiliary contacts are connected in series? All contactors have to be pulled it to get continutiy?

If so, it likely is the contact resistance that is causing the voltage drop - not the jumper resistance or the jumper connection resistance.

cf

 

[Chamuit]

Can you use powerblocks? Feed between them with larger conductors between the blocks to prevent voltage drop.

 

[broadgage]

If all 100 contacts are in series, then as suggested by others voltage drop in the contacts may be an issue.
To an extent, this may be compensated for by raising the control supply voltage a little.
For example if the equipment is designed for 120 volts +/- 10%, and the actual voltage is exactly 120 volts at the source and 110 volts at the far end, then increasing the control voltage to 132 volts should help.

It sounds like a large and complex piece of equipment if it contains 100 contactors, and a check should be made that any transformer(s) used for control supplies are big enough, and that the correct tappings have been selected.
If each contactor coil is 10VA, then the total load is about 1,000VA, plus any relays and pilot lamps etc. By control circuit standards that is a lot, and may require at least #14 wire, rather than the smaller wires normally used for control circuits.

 

[petersonra]

The contacts are in parallel. The voltage drop is not a whole lot (maybe 1/4 volt), but it is enough that the equipment is out of spec.

I don't have any control over the input voltage. Thats part of what is being tested.

The coils are fine.

Only one of the 100 contactors can be on at a time, but when it is on 32A flows through the chain. 32 amps through 200 connections.

 

[wireguru]

what gauge wire and what type of terminal on the contactor?

 

[StephenSDH]

The voltage drop is not a whole lot (maybe 1/4 volt), but it is enough that the equipment is out of spec.

Easiest thing would be to rewrite the spec.

Not 100% sure I understand you situation, but you might want to consider power distribution block(as noted above) and breaking up the chain into groups with home runs to the distribution block.

 

[petersonra]

Easiest thing would be to rewrite the spec.

Not 100% sure I understand you situation, but you might want to consider power distribution block(as noted above) and breaking up the chain into groups with home runs to the distribution block.

I can't really change the spec.

Rewiring the thing is kind of a pricey option. But its looking like the only option.

 

[mivey]

The contacts are in parallel. The voltage drop is not a whole lot (maybe 1/4 volt), but it is enough that the equipment is out of spec.

I don't have any control over the input voltage. Thats part of what is being tested.

The coils are fine.

Only one of the 100 contactors can be on at a time, but when it is on 32A flows through the chain. 32 amps through 200 connections.

What is the voltage drop assuming loss-less connections?

 

[LarryFine]

Only one of the 100 contactors can be on at a time, but when it is on 32A flows through the chain. 32 amps through 200 connections.

I would use that multi-contact pathway to supply a single contactor for that 32a load. That way, only the coil current will flow through the 200 connections.

 

[Cold Fusion]

The contacts are in parallel. The voltage drop is not a whole lot (maybe 1/4 volt), but it is enough that the equipment is out of spec. ...

...Only one of the 100 contactors can be on at a time, but when it is on 32A flows through the chain. ...

.25V at 32A -> .008 ohms. 8 miliohms puts you out of spec. This will be tough.

What is the max Voltage drop and still be in spec? This will give you the max loop resistance.

What is a nominal contact resistance? Hopefully you have a dlro.

...Rewiring the thing is kind of a pricey option. But its looking like the only option

yes

cf

 

[Cold Fusion]

I would use that multi-contact pathway to supply a single contactor for that 32a load. That way, only the coil current will flow through the 200 connections.

Excellent design choice. Good idea.

cf

 

[Jraef]

The contacts are in parallel. The voltage drop is not a whole lot (maybe 1/4 volt), but it is enough that the equipment is out of spec.

I don't have any control over the input voltage. Thats part of what is being tested.

The coils are fine.

Only one of the 100 contactors can be on at a time, but when it is on 32A flows through the chain. 32 amps through 200 connections.

Most IEC contactor manufacturers have what they call "star bridges" or "paralleling links" that are standard accessories for the contactors, where the spacings match up exactly to the power contacts and they can be solidly bolted to the terminals. Most come as 3 pole to short all three contacts together (for use in Star-Delta starters) but can be easily modified by clipping one pole off.

 

[Besoeker]

The contacts are in parallel. The voltage drop is not a whole lot (maybe 1/4 volt), but it is enough that the equipment is out of spec.

A 1/4 Volt in how many? That seems like a very tight tolerance if it is a common supply voltage?

Only one of the 100 contactors can be on at a time, but when it is on 32A flows through the chain. 32 amps through 200 connections.

I'm probably missing something here otherwise I'm sure others would have already commented.

If the contacts are in parallel and only one contactor is energised at a time, then the current would pass through just one contact. Sure, if the circuit being switched came in and out at the one end of the physical arrangement of the contactors and the one making the contact closure is at the extreme other end then yes the current would down one set of 100 connections and back up the other. But that would be the case in just that one situation.
Maybe the circuit to be switched could come in half way down the chain and that would, for worst case, mean it would have to pass through 100 connections.

Different practices, I know, but we never use solid wire on contactors (or any panel wiring for that matter). We use flexible/stranded and a crimp connector. I have seen solid used in the past but I have reservations about it.

 

[StephenSDH]

I'm probably missing something here otherwise I'm sure others would have already commented.

If the contacts are in parallel and only one contactor is energised at a time, then the current would pass through just one contact.

I think he is saying that the current is only flowing through one contact, but if contactor 100 closes the unswitched conductor is jumpered across the top of 99 contactors.

Is there any codes against ring powering the circuit inside a control panel? That could reduce the impedance significantly. I see this quite often, but not on purpose.

 

[Besoeker]

I think he is saying that the current is only flowing through one contact, but if contactor 100 closes the unswitched conductor is jumpered across the top of 99 contactors.

But if the unswitched conductor was connected to contactor 50, the current would be jumpered across 49 rather than 99 contactors.

 

[LarryFine]

I would use that multi-contact pathway to supply a single contactor for that 32a load. That way, only the coil current will flow through the 200 connections.

Excellent design choice. Good idea.

cf

Thanx, F.C.

 

[Smart $]

I can't really change the spec.

Rewiring the thing is kind of a pricey option. But its looking like the only option.

Are you saying there is only one set of contacts contributing to the voltage drop?

Is the line and load connected to the end of the jumper chains (near-near, near-far, far-near, far-far)? You can cut the jumper VD in half to one-quarter by connecting line and load in the middle of the line and load jumper chains.