Suppose this contactor by Schneider LC1D115.

enter image description here

I don't understand why it has a lower withstand current for signaling circuits when it can handle 10X the amount of current for power circuit on the same amount of time.

Signaling circuits from what I know are some sort of industrial lights that will be powered on/off by these contactors.

How are they different from power circuits? One would think that power circuits such as driving motors are more strenuous than powering lights.


3 Answers 3


(Trying to state more clearly what KASPAROLDENDORFF already said)

This contactor has two sets of contacts:

  1. Power circuit, consisting of 3 normally open contacts.
  2. Signalling circuit (also called auxiliary contacts), consisting of a pair of 1 normally open and 1 normally closed contacts.

You would use the power circuit to control the main load. You could use the signalling circuit to control lamps or some auxiliary equipment. Often it is used for signalling that the contactor is now active, or to activate other contactors. It can also be used to implement relay logic functions, such as making the contactor latch on/off with a pushbutton control.

  • \$\begingroup\$ Ahh so that what it means. Thank you very much for clearing that up \$\endgroup\$
    – Jake quin
    Jul 19, 2021 at 17:14
  • 3
    \$\begingroup\$ Thanks for this input. Sometimes what you take for granted is a mystery for others. That is why we have stackexchange in the first place. \$\endgroup\$ Jul 20, 2021 at 6:17

This signal rating is for ITS signaling circuit. Not if used in signaling circuits as this type of contactor will most definitely not be used for that purpose. Its coils should be energized when you need to switch on some machinery, closing the contacts and providing the power for that machine.
Green - Signaling / Red - Power / Yellow Coil / ConnectiondiagramLC1D115M7

  • \$\begingroup\$ You mean the one activating the contactor right? but why would they reach those currents? dont they have inbuilt current limiting? \$\endgroup\$
    – Jake quin
    Jul 19, 2021 at 7:16
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    \$\begingroup\$ If you're not used to this type of contactor it's not obvious that 'signalling' applies to the auxiliary contacts not the main contacts, might be worth adding that to the answer \$\endgroup\$ Jul 19, 2021 at 14:20
  • 1
    \$\begingroup\$ I would lead off the answer by saying that the contactor assembly has two kinds of contacts: high-current contacts whose purpose is to switch large loads, and smaller contacts whose purpose is to either operate panel lights or signal to industrial control equipment that either all of the high-current contacts are closed, or none of them are closed. \$\endgroup\$
    – supercat
    Jul 19, 2021 at 15:59

Because these are different tiers of contacts

These aren't different ratings for different signals on the same contacts. These are a totally different set of (auxiliary/signaling) contacts.

You'll have the 1-3 main contacts which connect the live phase(s).

Then it's very typical for contactors to have a number of "auxiliary contacts". This can be signal lines that carry low voltages to SCADA systems (hence the name) to indicate the position of the contactor, or it could be lower power accessory appliances:

  • a dust collector that starts up with a big milling saw

  • a coolant/lubricant pump that starts up with a CNC cutter head

A machine that takes 500A of 480V could conceivably have a 100A accessory. I've seen an industrial wood chipper that had a dust collector about that size. (The dust collector sat on top of a semi-trailer).


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