NEC or IEC Standards and Indicator Lights

[amptramp]

Hello all,

I am investigating the application of a "power on" indicator lamp for machine control. I am interested in any code references in any standard that explicity discusses the application.

Specifically:

1) Is a "power on" indicator light required for machine control?

2) Is a "power on" indicator light considered part of the power circuit or is it part of the controls circuit, i.e., NFPA 79 Section 3.3.75 states that power circuits are used for "productive operations". The power for the indicator light is fed from the load side of the main machine UL489 circuit breaker (25A).

3) What size wire should feed the indicator light? Current review of NFPA 79 - Electical Standard for Industrial Machinery (7.2.3 and 7.2.4) dictates the wire size for control circuits to be no smaller than 14AWG when the conductors leave the panel enclosure (and they will as the indicator is typically mounted remotely from the controls cabinet); however, for power circuits the wire size should be 10AWG (25A circuit). Either conductor size seems silly for a single indicator light.

 

[jraef]

There are no "standards" that dictate the use, or non-use, of any indicating lights. That is strictly an engineering decision. If you want one or feel it is necessary for your operation, by all means install it. What it means and how it is connected is strictly up to you.

As to the wiring, yes, NFPA 79 dictates the wire sizes as you observed. If your power indicator light is connected directly to the line power source, then the 10ga would apply because the conductors are leaving the originating enclosure. If it is on the secondary of a control power transformer or power supply, then 14ga would suffice. I will add however that running line power out through a conduit just to indicate Power On is a bit of overkill. I would use the Control Power for that, it would tell me not only that the disconnect is closed, but also that the control power is present. An exception would be if you have separately sourced control power.


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[jraef]

I should have clarified: NEC. I am not familiar enough with IEC standards to address that.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376