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2nd Year Apprentice here.
Me and a journeyman were pulling new wires for existing fixtures at a hospital. She had the circuit turned off. When we finished, she went to the panel to turn the circuit on. She turned it on, but the lights didn't kick on. When she noticed this at first, she was nervous, thinking that maybe she missed something - when she then said, "Oh, I forgot to turn the relay on". She then went to go turn it on, and everything came on.

My question. What are relays used for lighting circuits for? Why do commercial projects use them when you can essentially do without them and just use the breaker only to turn the lighting circuit on and off.

2nd question - Are ~EM~ lighting just a term used for lighting that will ALWAYS stay on? (Meaning that they are treated like receptacles . . . having no switch to turn it on and off?)

3rd question - If so, how are some receptacles designated as on the EM circuit? Whats the difference between an EM receptacle and a regular receptacle.

4th - I've noticed that some people in this thread can be A-holes against people who ask questions. They either do this for attention, or to put the other guy down. Fair warning for such individuals - I couldn't care less if I tried on your opinion. I'm trying to learn - and get a life.

For those of you who like to help - thank you very much - and your answers are deeply appreciated.
 

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My question. What are relays used for lighting circuits for? Why do commercial projects use them when you can essentially do without them and just use the breaker only to turn the lighting circuit on and off.
You can control a relay (more likely a contactor, which is more or less a bigger, heavier duty relay) with a lot of different devices. A common application is to use a photocell to detect ambient light levels and automatically turn the relay (and thus the lights) on when it gets dark. You could also use a regular light switch to control it, or a lighting control panel, or another relay, etc. etc.

Circuit breakers being used as switches for fluorescent or HID lighting have to be specially marked with "SWD" or "HID"

2nd question - Are ~EM~ lighting just a term used for lighting that will ALWAYS stay on? (Meaning that they are treated like receptacles . . . having no switch to turn it on and off?)
As in emergency lighting? Yeah typically it is fed with straight power, and often employs some sort of battery backup power source to provide egress lighting if the power goes out. If it's in a hospital it might involve that as well as be supplied from the hospital's backup power system (likely a generator).

3rd question - If so, how are some receptacles designated as on the EM circuit? Whats the difference between an EM receptacle and a regular receptacle.
If you're at a hospital, it probably means that they are supplied from the facility's backup power system. Check out Article 517 in the NEC and you'll see how a health care facility's power system is required to be divided up for emergency loads, critical loads, etc.

4th - I've noticed that some people in this thread can be A-holes against people who ask questions. They either do this for attention, or to put the other guy down. Fair warning for such individuals - I couldn't care less if I tried on your opinion. I'm trying to learn - and get a life.

For those of you who like to help - thank you very much - and your answers are deeply appreciated.
**** you.
 

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God-fearing Volt-head
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3rd question - If so, how are some receptacles designated as on the EM circuit? Whats the difference between an EM receptacle and a regular receptacle.
Any red receptacles or red light switches are also on an emergency stand-by system. The NEC article quoted is a great place to start looking for answers, though, as mentioned earlier.

:thumbsup:
 

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I've noticed that some people in this thread can be A-holes against people who ask questions. They either do this for attention, or to put the other guy down. Fair warning for such individuals - I couldn't care less if I tried on your opinion. I'm trying to learn - and get a life.

Their are one or two A holes as you describe them, but remember old school electricians expect that people playing with electrical wire should at least have some basic understanding of what they are doing and the dangers associated with what they do.
Thats the way they were trained, and it's now the way they are.

The old saying " A little knowledge is a dangerous thing"
very apt for electricity.

So if you stay in your depth and ask questions nicely you will mostly always get a good answer.
But if your clearly out of your depth and intending to do stupid things
without realising the dangers then they will get there backs up real quick.

Ignor the few who are not nice, as they are the minority !

P.S. the older members really have taken in a lot of knowledge
over the years, so they are a valuable resource of information
which you can tap into.

Ask and learn
WELCOME

:thumbup:
 

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Any red receptacles or red light switches are also on an emergency stand-by system. The NEC article quoted is a great place to start looking for answers, though, as mentioned earlier.

:thumbsup:
While that is common, the code does not restrict the use of red, or any other, color devices. I have seen projects where the red devices were specified by the interior designer and it was not because they were being fed from emergency circuits.
In some areas a red switch is used as the required oil burner disconnect switch.

I guess what I am saying is that you should never just use the color to identify anything associated with an electrical system and and includes wire colors.
 

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God-fearing Volt-head
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While that is common, the code does not restrict the use of red, or any other, color devices. I have seen projects where the red devices were specified by the interior designer and it was not because they were being fed from emergency circuits.
In some areas a red switch is used as the required oil burner disconnect switch.

I guess what I am saying is that you should never just use the color to identify anything associated with an electrical system and and includes wire colors.
Agreed, but I limited the scope of my comment to hospitals and not other areas, then referred the guy to the NEC. I've never been in a hospital that red switches/receptacles didn't indicate emergency powered devices. I guess, though, it could change.
 

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2nd Year Apprentice here.
Me and a journeyman were pulling new wires for existing fixtures at a hospital. She had the circuit turned off. When we finished, she went to the panel to turn the circuit on. She turned it on, but the lights didn't kick on. When she noticed this at first, she was nervous, thinking that maybe she missed something - when she then said, "Oh, I forgot to turn the relay on". She then went to go turn it on, and everything came on.

My question. What are relays used for lighting circuits for? Why do commercial projects use them when you can essentially do without them and just use the breaker only to turn the lighting circuit on and off.

2nd question - Are ~EM~ lighting just a term used for lighting that will ALWAYS stay on? (Meaning that they are treated like receptacles . . . having no switch to turn it on and off?)

snip
Since the other questions have been answered well, I will point out that EM lights are not always hot. They are often switched on and off like any other lights but when the power goes off they come on automatically with the emergency power. The Bodine GTD20A is a relay device designed for just that purpose. When regular power is on, the lights can be turned on and off with the wall switches but when regular power drops out and the emergency system kicks on the lights come on and the switches no longer operate the lights.
 
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