Electricians-or any others – lil help?
Got a quandry and I am trying to figger out . . . .
I need to know if there is some way tp test test amperage rating of a circuit without seeing the breaker or the wire feeding a duplex. (Other than loading it up and seeing when the sparks fly smart-aleks. . . . .)
You see, I am part of a club that sets up in large convention buildings and we need A LOT of power for the operation. Like 3 or 4 20A circuits. Problem is we can’t tell, sometimes circuits are 15A sometimes 20, sometimes they have skinny breakers and are only 10A. Is there a tool that we can plug in that will read an amperage rating? Is there some way I can test using a digital multimeter?
I know something about electricity, but this one has me stumped. And it would be nice to plug up knowing how much power is there before we have to track down a thrown breaker. And we cannot visually inspect wire guage since it’s all encased in metal conduits.
Replies
There is no way to know without tripping the breaker.
10 amp breakers would be really strange.
AFAIK there is no place in the code that would allow them for general purpose 120v receptacles, but it might be hidden in there some place.
I guess my advice would be to assume all of them are 15 amp.
But another problem that I see is that you might not know which receptacles are on which circuit.
Or do they usually only have one circuit per receptacle (or duplex).
Thanks Bill.
You're right we don't know which duplexes are on a given circuit and it's all encased in metal conduit so it's not really possible to trace visually. Lots of J boxes between load center and outlets.
Thanks anyway, we'll continue with the plug in and **POP** method. Problem is-our lighting alone needs 30A minimum.
Thanks anyway.
30 amps for lighting? Time to split that load somehow. So you can be compatible with more recepticles.
If you pop open the recepticle and it is 14 gauge wire, then it should be protected by a 15-amp breaker. If is it 12-gauge wire, then it could be 15 or 20-amps. More than 20 amps and it should be a special recepticle. With one or two of the blades turned 90 degrees.
You have a limited ability to check for other users of that circuit by testing the voltage on the line. Either look between hot and neutral one different receptacles. An outlet with 114 volts likely has a good current draw on it already (10 or 15 amps) versus an outlet with 119 or 121 volts. Or look at the voltage between neutral and ground. A volt or two suggests no big users on that circuit. 3 or 5 or more volts suggests (but doesn't prove) a large current draw. All of this is effected by wire run length. A few hundred feet of wire run between the distribution panel and the outlet and this approach will work pretty well. 10 or 40 feet of wire and it won't work so well. Other effects dominate then.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
Checking voltage at the receptacle would only be valid if you knew what it was at the breaker. It could be 114 V. both places under no load, if that's what was coming from the utility. Nominal plus or minus 5% at the service entrance is what our DWP says they give us.
The hard part for this guy is knowing which receptacles are on which breakers, and what other loads may be in use -- or get turned on -- on the same circuits.
-- J.S.
Agreed. That's why I implied, but probably didn't make clear enough, that one should compare circuits on the same service. If most are 118 and 119 volts, for instance, 114 volts on another outlet strongly suggests line loss due to current draw on that circuit.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Tasco used to have a tool called the inspector which would simulate a 10,15, or 20 amp load and measure voltage drop etc,
Ask the maintenance man?
I had an electrician friend who was involved in an Easter Passion Play.We made up a neat little temporary board that he could take to just about any church and plug/n/play.I'm not sure of your total load or how often you travel ,but you might think of taking your own power set-up with you, instead of depending on local branch circuit conditions.
If you are setting these things up in a hotel or a convention facility... the Chief Engineer will have the circuits mapped. Common issue for a convention hotel... "can I run my display off this outlet?".
Most of the time, however, these facilities will have a vendor that you are required to use for electrical work. They will run whatever you request... for a fee of course.. a substantial fee... OK, for a fee that is downright outrageous! However.. the contract is the contract. And most facilities will not deviate from that contract... especially with electrical. Huge liability issues.
Unless your electrical needs are just what can be achieved through wall outlets... most likely you will have to contract for the additional power needs.
We're a modular railroad, not big time exhibitors or anything. The building we set up in is named the "cow palace" becuase its used during the MD state fair to house. . . . . well, cows. The wiring is a mess. No maps. No Chief engineers or maintenance men. And different duplexes may or may not feed off of the same breaker. Finding sufficient power is enough to give a man a headache. We run 4000 watts of incandescent light and haven't even started a train yet . . .
Thanks for the ideas though, I will take them with me to the next show.
For anyone interested, here's the club website:
http://www.fcsme.org
Given that...
I am a fan of the "portable box" idea for your application. Set up the circuits on your own box... then have the electric fed to you via a main line. You'll probably need to get a UL sticker on the setup.. but that is not a big deal (if you follow their guidelines).
This way... you control the circuits and only have to pay for the single... bigger... electrical line to be run. Single up-front expense that will save many $ and mucho time over the long-haul (get it?... "long-haul"... trains... har-d-har).
FWIW, stringing extension cords all over the building will probably cause you a problem with the fire-dude.... let alone the fact that it is not safe.
There's one test instrument that'll safely trip a branch circuit breaker--the "Circuit Breaker Analyzer 1000" from KO Instruments.
See their website at:
http://www.koinstruments.com/
Once you've tripped the breaker, you go to the panel and can see what it's rated.
The CBA-1000 tests the voltage drop in the circuit first, and does additional testing to make sure that the circuit can stand a direct short. It also aborts the test if the breaker doesn't trip at a safe current/time combination.
The voltage drop results would be valuable information for you in itself; you wouldn't want your set-up getting lost in a fire due to crappy wiring in one of the places where you put it on display.
Keep in mind that when you're using the KO unit, you're dropping a dead short across a 15 or 20 amp circuit. In conduit, the magnetic field from the high current (like 500-600 amps, for 20 to 100 milliseconds) causes the conductors in the pipe to really whip around. It's unnerving at first to hear clanging and banging in the walls; it sounds like the Ghost of Christmas Past rattling his chains.
So you could use the CBA-1000 to trip the breaker and so identify it, and determine the the breakers ampacity that way.
On the other hand, have you thought about using a (much less expensive) circuit breaker sniffer to I.D. the breakers? I just saw one by Triplett and it looks very reliable. You plug in the sender, then at the panel, run the receiver over all the breakers first, to calibrate it. The second pass over the breakers give a very clear-cut indication of which circuit the sender unit is plugged into.
Come to think if it, if you're running all that equipment, you ought to know which breakers are supplying it. Just in case you need to cut power.
Good luck.
Cliff
p.s. If anyone suggests shorting out a circuit (with a piece of heavy copper wire) to trip the breaker, ignore 'em. It's an extremely risky thing to do, both for the person doing it and for the building. C.
Edited 3/10/2005 6:55 pm ET by CAP
If you are always at the same location then diffently make up your own panel if ther is a place the you can get to connect it.Otherwise get a couple of guys with some of the cheap walkie talkies and plan a work day and make up a map of the outlets and what breakers that they are on.
One test I can think of is to use your meter to measure the voltage [if any] between the hot slot [the small one] of different receptacles. If you get 240 volts or so, then they are on different phases. If 0 volts they would be on the same phase but may be on different circuits.
If you can find two receptacles on different phases, you could divvy up your 30 amp lighting load into two more or less equal 15 amp loads and plug one into each receptacle.
Most commercial wiring would be on 20 amp circuits or at least #12 wire.
Railroading? What does a locomotive draw? Something like 480 volts and 1000 amps?
~Peter
1. What color is a green ground screw?2. To trip a circuit breaker, you must stick out your foot as you walk by it. T or F3. A keyless fixture cannot be unlocked? T or F4. A circuit breaker reads "20" on the handle. This means it can trip only 20 times before it wears out. T or F5. A flush mount device may only be hooked up to a toilet. T or F6. An Ohm is a Hindu measurement of voltage. T or F7. Electrical inspectors are known as ________.8. If you have a molded-case circuit breaker, the mold can be washed off with warm soapy water. T or F.9. What type of bender is needed for 3/4" flex? _________
If you plugging into a receptacle with the little smiling face configuration we all know and love it is either a 15 or 20A circuit. Best way to find out which would be to check the beaker. Get friendly with the buildings custodian/s. Always a good move as they can provide benefits in access, storage, power.
Even given a dummy load, a couple of blow driers with an ammeter clamped on would do it, it would be hard to tell. A 15A circuit can carry 20A for a considerable time, inverse time breakers are typical and these can handle fairly large overloads for short periods without tripping, and an older, worn out, 20A breaker might trip at 19.5A.
What I would do is act as if all the circuits were 15A. Arrange the loads to draw only 12A, no need to be too particular, so you have some headroom. Subdivided like that you ask for more circuits but what you get you can count on.
You can also practice some load control if possible. A lot of display units use a incandescent bulbs that are inefficient, a potential danger for fire and make the area around them uncomfortably hot. This later point can be an advantage in cold climates or over conditioned exhibition halls. Often substituting compact florescent can drastically lower the amperage pulled.
get a circuit tracer and that way you can tell what breaker feeds that receptical. Wouldn't tell you how many recepticals though unless you just check em all.