Electrical problems at home related to RPC

They can be turned off, however it requires pulling the meter. You really really don't want to be holding onto the inadequately insulated end of an Allen wrench that is at 120v relative to ground and has essentially no current limiting or fusing.

Pete C.

Not really. But the scary bit is grounding the Allen wrench, or any tool, at even 100 Amps. Can you spell KAAAAH POOOOOOWWW ?

Take care.

Brian Lawson, Bothwell, Ontario.

ps... Oh that is funny.!!! My spell checker wants to speel that as "BOO BOO"

What a hoot! A computer that makes Freudian slips!! Ha ha ha.

LOL!! You beat me to it! Greg

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You'll get far more than 100 Amps, even if it was after the breaker. The breaker won't limit the current, only shut it off when it's over 100 Amps and it's not instant either. Pre breaker it will just max out whatever it can with the voltage drop from the feeders until something melts open.

Pete C.

That's a nice story. In my case though, the RPC runs on 220V, so neutral is not a big deal aside from the control circuit. Loose hot mains wires at the power panel could possibly (but not very likely) account for dimming lights.

i

On Thu, 12 Jan 2006 21:44:40 GMT, with neither quill nor qualm, Ignoramus18851 quickly quoth:

A pair of rubber/nitrile/latex gloves and a length of shrink tubing on the allen wrench should do the trick, eh?

My parents' house in LoCal had some lights doing that and I never did check the panel. I pulled the outlets and checked them for tightness but didn't follow them back to the source. The panel was outside locked up somewhere. Maybe I was afraid because I knew it was one of those lovely aluminum jobs...

Could be also - you have a 200 amp box - and share a transformer with 3 other houses - each with 200 amp boxes. The pole (example only) can supply 400 amp max - and never expects to see more - much less 800 amps. Now the neighbor installs an electric heater. Another installs a monster TV and ... another adds a pool pump and a spa... So the transformer might be on the edge and you brown out the transformer!

I'd take off the panel cover and verify the mains screws - carefully.

Martin Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder

Ignoramus18851 wrote:

This happened to a boss of mine in the 1970s, in the suburbs of Washington, DC. He complained of weird interactions between circuits that ought to be independent, which suggested bad ground to me. So I visited his house one saturday. It turned out that the electrician's helper had never gotten around to tightening all the screws down onto the wires; nothing was tight. It worked at first, then the wires gained a little corrosion.

Many years later I went to a summer stock theater that my kid sister was in, held outside at a local school. While waiting for things to start, in the late afternoon, I'm idly looking at the lighting setup (I used to work theater lighting). Then I notice how *blue* the light from some of the unfiltered stage lights seem. Blue? How do you do that - it takes overvoltage. Hmm. They will have a three-wire 220-volt feed; the neutral must be open. How else could this happen? So I went to the director and asked him if he had been having problems with lamps burning out too soon. Yes! Solid-state dimmers too. Expensive. And how did you know? Tell blue story. We look at the cabling. Sure enough, in one of the Edison connectors, the neutral was loose. Tighten the screws. Director is very happy, because now he can prove that the dimmers blew because of bad cabling supplied by the rental company, and the rental company pays, not the director. Not exactly a damsel in distress, but he'll have to do.

Joe Gwinn

Additional starting capacitance would probably help. You might also try power factor correction capacitors directly across the motor windings connected to the single phase supply.

Don Young

If you have a 100 A or less service, or this problem happens when you already have a heavy load operating, like an oven, electric clothes dryer, etc. then there may be nothing you can do, given that service. You noted the RPC, alone, draws 120 A at startup.

If you have a 200 A or greater service, and the problem happens when no other heavy load is on, then there is just plain something wrong, and it could be dangerous. A loose connection somewhere between the transformer and breaker panel is a strong possibility.

One possible way to isolate high-resistance connections is to check the voltage at the RPC's breaker when it is started. If the nominal

240 V dips below, say, 200 V, that indicates a lot of loss. Work backwards toward the service entry. If the service entry drops to about the same level as the previous measurment, then the service has a high resistance, certainly too high for this load. If it DOESN'T dip much, then the problem is between the service entry and the load breaker. If you can spot some place where the voltage drop changes, like it is OK at the service entry breaker (if present) but dips at the main breaker panel, then the problem must be between these two points. Some of these main connections can be very hard to work on, such as requiring an allen wrench to tighten, so you really have to be sure the juice is off before touching it.

Jon

There are easier ways. One way is to rig a time delay relay, and start the converter on 120 V, then when it has spun up, have a double-throw relay (got to be break before make) switch it to 240. This will drastically reduce starting current. it will also take a little longer to start. If the simple way is too massive an unbalanced load on the breaker panel, then you could use a step-down transformer or autotransformer to make 120 V from the 240, and draw it balanced from both hot wires.

It is possible some motors won't rotate at half voltage. If so, you can use the traditional scheme of capacitors that makes the idler motor start faster on the normal voltage. It should allow the idler to start up at the reduced voltage.

It is fairly common on larger motors to use a Delta-Wye starting scheme to reduce the starting demand. The motor is connected in the WYE configuration to start, then when up to speed, the wiring is changed over by a relay to the delta configuration. (This of course requires a motor where both ends of each winding are brought out.)

Jon

Basically it's limited by the impedance of the source, typically back to a pole pig in residential service. That's low, but it's not really low.

Here at work they've been upgrading all the 20 amp breakers in the turret boxes in the labs to be over 100KA interupt rating.

Basically the 'distance' back to the 13.8KV feeders for the building is pretty low, from an electrical standpoint.

Jim

Right, so like I said, well over 100A until something melts open. Not a pretty thing.

Pete C.

A guess? Probably over a thousand amps peak.

Jim

Those things scare the HELL out of me, and I work on live 240 V gear all the time. I can't think of ANY safe way of tightening those, without making a special tool. If that L-shaped allen wrench touches anything else, like the electrical box, the explosion will be totally awesome, and you don't want to be anywhere near it. If you are not familiar with the term "arc flash" you might want to read up on it. A 240 V residental service doesn't really supply the watts that can get into serious arc flash territory, but it could still send you to the hospital.

Yes, here, too. The phenomenally incompetent guys that put in a water main managed to cut our phone service 4 times, the gas main once, and nicked the insulation on the buried electric feed. Water got in and ate the conductor. Somebody turned on the stove one day, and most of the lights in the house went out. The electric co. strung a bundle of #6 wire across our back yard and just left it like that for about SIX WEEKS!

Jon

Everything in my basement shop runs off a 100 amp breaker. I have a 30 hp rpc . A 15 hp cnc lathe a 10 hp cnc mill and 28 two bulb 8 foot florsent lights, When I start the 30 hp phase converter the upstairs lights dim just a little hard to notice . I would add some start caps,

The residential transformers are tested, I believe, to limit current to below

10,000 A. If they didn't, you couldn't use 10 KA max interrupting capacity breakers in your home panel. If 1000 A doesn't scare you, 10,000 really ought to! I have seen a 3-phase 400 A 240 V service at a motel short out during a building fire. It was like a ground display at the 4th of July! The fire department was working on the fire up to that point, but when white hot aluminum started cascading all over them, they ran for their lives!

jon