Customer Connections

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fifty60

fifty60

Senior Member
Location
USA
I have 15 customer event relays that a customer wants to have rated at 5A each. I will be connecting the relays to the output of a PLC, and the customer will then connect to the relay outputs.

What protection do I have to supply the customer? Are voltage/current ratings and yellow #16AWG wiring enough? The yellow wiring is meant to indicate that the conductors could still be live even with the equipment disconnected from the power supply...
 
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templdl

Senior Member
Location
Wisconsin
fifty60 said:
I have 15 customer event relays that a customer wants to have rated at 5A each. I will be connecting the relays to the output of a PLC, and the customer will then connect to the relay outputs.

What protection do I have to supply the customer? Are voltage/current ratings and yellow #16AWG wiring enough? The yellow wiring is meant to indicate that the conductors could still be live even with the equipment disconnected from the power supply...
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Interesting. Are the relays just triggering the PLC with a contact closure? What type of current is required to do that? The PLC is looking for a contact closed and open action only. I would be more concerned about the relay contacts themselves the they would be able to operate reliable considering the extremely low current that the PLC requires to detect when the relay contacts open and close.
With such a small current what is to be protected? Even if the relay contacts are rated at 5a what is the actual real life current?
 
fifty60

fifty60

Senior Member
Location
USA
The coils (with LED indicator) operate at 27mA. The PLC output has a separate 24VDC power supply connected to 15 normally open internal relays. When the "event" is selected on the HMI, the contacts close. For all 15 SPDT coils with LED's take a total of about 10W.

The SPDT contacts are rated at 12A, though I the documentation I will provide will state "5A" because that is what the customer requested.

It always concerns me to provided these dry contacts that will not be fused on my end. The only safety precautions I can take are the yellow wiring and the ratings in the manual....
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
this is a common practice. it is done on an almost routine basis.

I see no reason to relabel them as 5A contacts especially if you are going to use #16 wire on them.

Contacts that are interrogated by a remote source are normally protected at the source. A single 10A fuse at that end should suffice.

Yellow wire is a common color inside of control panels to denote that something may remain energized even with the panel's main disconnect open. It has no NEC meaning. If you want it to mean something inside your cabinet I suggest a nameplate that indicates what it means. Maybe with a notation that indicates the maximum OCPD size.
 
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