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Old 12-05-2011, 01:30 AM   #16
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Commercial Building with 277 Volt Exit & Emergency Lights


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Originally Posted by Stubbie View Post
I think one of the better myths is that high voltage will knock you away and break your contact.....I found this to be true with 480 .. once ... I hope there isn't a second time.
Research based on accident reports does indicate that this is true for voltages in the "medium voltage" range and higher (i.e. 4160V and up). One explanation that has been proposed is that a shock from that voltage range paralyzes all muscles equally, with no preferential contraction of the muscles nearer the current source, and thus causes no tendency to grab the conductor. Regardless of the reason, anecdotally, nobody gets locked up on a power line. Of course, you'd still rather get locked up on 277V than get knocked clear by 7200. At least your buddy can save you from the 277.

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Old 12-07-2011, 01:21 AM   #17
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Commercial Building with 277 Volt Exit & Emergency Lights


Exit and emergency lights can have either small batteries that look similar to "C" or "7AA" batteries, with or w/o leads. Some fixtures use 6V or 12V batteries. I have not seen exit or emergency lights with the inverters. Are they used on large systems?

One of our customers has some of the exit and emergency lights powered before the breaker box. No disconnects that have been found. They hired a real electrician, who wired the new fixtures hot. The electrician had never seen emergency lights wired like that either.
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Old 12-07-2011, 04:41 AM   #18
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Commercial Building with 277 Volt Exit & Emergency Lights


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Originally Posted by J. V. View Post
My point was all voltages can be deadly. Not just 277 volt and up. Of course the higher the voltage, the more damage can result. But this is a DIY site. Are we going to start telling everyone here that 120 volts is safe? But 277 is not safe?
Electricity is inherently dangerous regardless of voltage. That was my intention.
That was not the way it came across !
Anyway it was not my intention to be nasty,
But in my book more voltage generally means current,
Technically it is the currant that kills you, not the voltage,
And most technically minded people understand that,
So you are sorta right !
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Old 12-07-2011, 12:22 PM   #19
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Commercial Building with 277 Volt Exit & Emergency Lights


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Originally Posted by dmxtothemax View Post
But in my book more voltage generally means current,
Technically it is the currant that kills you, not the voltage,
And most technically minded people understand that,
So you are sorta right !
Increased voltage means less current. And you are right. Technically minded people know this.

Last edited by J. V.; 12-07-2011 at 12:48 PM.
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Old 12-07-2011, 02:49 PM   #20
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Commercial Building with 277 Volt Exit & Emergency Lights


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Originally Posted by J. V. View Post
Increased voltage means less current. And you are right. Technically minded people know this.
Ok, come on. Really? I certainly hope you know that's only true in a handful of unusual circumstances like AC motors and constant-power electronic devices. For everything else, including humans, ohm's law applies and there is a direct linear relationship between voltage and current.

http://en.wikipedia.org/wiki/Ohm%27s_law

Even an Ugly's Guide explains this.
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Old 01-19-2012, 07:13 PM   #21
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Commercial Building with 277 Volt Exit & Emergency Lights


Sorry for the long delay in response. The building management contacted a total of three licensed electricians to fix the problems. The first said the wiring was all wrong and offered to rewire the building including new conduit and wire for about $7500. The second offered to disconnect the existing exit an emergency light circuits while still hot and run new 120 volt feeds from nearby office and convenience outlets for about $1200. (He said he would put wire nuts on the existing 277 wiring, but had no idea how to disconnect it.) The third, an older union electrician about to retire suggested we do our own detective work and map out conduit runs above the suspended ceiling, etc. No removal of covers, just map out where they seemed to go. After mapping out what we could, he would return to see what we had found. We spent about 4 hours with two people doing the survey and discovered one conduit run that did not go to an emergency light or exit sign. The electrician found that this went into the power companies sub-station on the side of the building. The power company came out and opened the door and right on the wall next to the door was a fused disconnect switch prominently labeled "Exit Signs". This was feed directly from the substation equipment just after the metering equipment. The power company employee verified with his supervisor that this was a common practice in the "old days" so that nothing the customer did could turn off the exit signs. The customer did not have a breaker or fuse he or she could accidentally remove which would render the signs inoperative. The signs would only fail in the event of the failure of the electric companies service. We were told that this was a common practice in the days before battery back-up signs. The electrician came back a few days later and replaced the defective signs with new battery backed-up signs after arranging to have the substation unlocked so he could turn power on and off as needed. Total bill for labor -- $127. The electrician had never seen this arrangement before, but checked with the inspector and local fire marshal who said it was legal in our area.

Problem resolved.
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Old 01-19-2012, 07:26 PM   #22
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Commercial Building with 277 Volt Exit & Emergency Lights


Thank you for the follow up !
It is interesting what you found !
Now we all know a little bit more !
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Old 01-19-2012, 07:37 PM   #23
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Commercial Building with 277 Volt Exit & Emergency Lights


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Total bill for labor -- $127
What an awesome deal!
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Old 01-19-2012, 08:25 PM   #24
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Commercial Building with 277 Volt Exit & Emergency Lights


Did you find out why all the exit signs went dead as you mentioned in the first post?
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Old 01-20-2012, 09:33 AM   #25
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Commercial Building with 277 Volt Exit & Emergency Lights


The cause of the Exit Light Circuit failure was a burnt-out transformer in one of the exit signs. This caused the 15 amp fuse in the Power Company sub station to blow. Once the "bad" exit sign was disconnected, the power fuse was replaced and power to the remaining lights was restored. Several of the exit signs of a similar design were replaced at the same time. All in all, it took almost a week to get all the signs working again.

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