electrical ghosts

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binney

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1st the details
15,000 sq ft. building
1/2 offices 1/2 shop
New building in a new industrial park.
120/208 3ph 200 amp service
QO Panel


Here's the problem/ problemssssssssss.

1. if you plug a saw into any of the outlets within a 150' of the panel the saw instantly trips the breaker. If you plug a 100' ext cord into the outlets, and then run the saw, it won't trip the breaker.

Amp probe shows 10 amps (+ or -) at start up for the saw. Volt drop to 116 volts +/-.

Nothing out of the ordinary..............

2. Breakers keep tripping for no reason. 1 row of L-bay lights tripped yesterday ( 4 lighs per circuit 120v, 14 amps on the amp probe, no VD)

The air compressor trips, the pressure washer trips, the office lights trip, some of the circuits barely even show up on the amprobe.

It doesn't matter what ph there on.

I checked all of our connectios in the panel, i've put loads on the service to check for VD I've checked amps.

I give up!!!!

It has to be on the utility company's end!! Right??? Nuetral problems??

Or is it a ghost.
 
Re: electrical ghosts

The really strange part is the use of an extension cord that doesn`t trip the breaker.Any ideas from others as to why this occurs,I`d like to know for my own info :confused:
 
Re: electrical ghosts

I'm guessing that the problem is "loose neutral" based, and the extension cord was plugged into a receptacle from a phase that didn't experience drop during the loose neutral event. Alternately, could be a loose hot that only shows up intermittantly.

I'd get a Beast of Burden or other load bank hooked on this MDP right away and see if it is a loose neutral or maybe just a loose hot. I'd bet you a cup of coffee it's one of the two and nothing especially exotic.

[ November 01, 2005, 10:18 PM: Message edited by: mdshunk ]
 
Re: electrical ghosts

Please clarify one aspect for me. Call this a litmus test for ghostliness.

Plug the saw into a receptacle near the panel. It trips the breaker. Now plug a 100 foot extension cord into that same receptacle, plug the saw into the extension cord, and turn it on. Does this trip the breaker? Is that what you had tried to describe?
 
Re: electrical ghosts

that's exactly it! As far as being one of the phases, it occurs on all 3 ph's, that's what makes me think it's a nuetral.

I tried tightening all the connections, but nothing seemded loose.

I'm going back first thing tomorrow, AGAIN.
 
Re: electrical ghosts

Have you considered voltage drop on extension cord?

What is the guage of conductors?
What is saw size and current draw?

150 foot cord R will be 50% more than that of 100 foot.

IR drop will be 50% more
BUT the saw wants to start
(it is not just a resistive load)
therefore draws more current?

At least you have checked to see if breakers will trip.
 
Re: electrical ghosts

there's definetly v drop,

If the voltage drops amps go up.

So why do i need to ADD 100 + of cord to get the breaker to hold?

The longer the cord, the higher the amps. I've had my ampprobe and volt meter on for both scenerios. Neither the volts nor the amps changed much. Right around 10 amps.
 
Re: electrical ghosts

This is not behaving like a loose anything. If it consistently trips when the saw starts, and if it consistently does not trip with the extension cord plugged in, then whatever has set this up is there, and does not come and go like a loose connection would do.

I would have asked about using a different saw, except that you mentioned all the other things that trip their breakers.

Just for the record, are any of these breakers GFCI or AFCI?

Also for the record, is the circuit that is tripping when you plug in the saw a multi-wire branch circuit?
 
Re: electrical ghosts

High available fault current. Is this service very close to the utility xfmr? It may have an exceptionally high fault current which instanously trips the breaker, but with the long extension cord it reduces the available fault current at the saw thus giving the breaker another mil second or so for the current to drop back to normal levels. Have you tried a linera load like a 500 or 1000 watt light?

I dont know maybe I am way off here.

[ November 03, 2005, 07:30 PM: Message edited by: mikeames ]
 
Re: electrical ghosts

Ummm.. the available fault current won't trip branch breakers. You only concern yourself with the available fault current when you're making sure that your equipment won't explode during a big fault.
 
Re: electrical ghosts

What limits current the instant a motor starts. Not the second the mili second??? The only limiting factor is the systems impedance. Increase this by adding 100 feet or so of extension cord and all is well. Take it away and the CB sees an inrush that is unlike normal inrush since the panel is so close to a very large xfmr. No I agree it usually does not trip branch breakers but stranger things have happened. If both breakers the Main and the branch both have the same rating then its just a matter of which goes first.
 
Re: electrical ghosts

Available fault current has nothing to do with inrush currents. The impedance of the source has nothing to do with limiting inrush currents except in those very rare occasions when the source is "power limited" (i.e. a class 2 transformer).

Yes, the impedance of the extension cord will reduce the impact of the inrush current from the saw.

When you are measuring voltage drop are you doing it at the load or at the panel?
Are you using a true RMS ammeter? Most ammeters are averaging types and are not fast enough to see true inrush currents.

The 15 and 20A 1 pole QO breakers have a "quick open" design (no that is not how the QO family got it's name). This design trips on currents as low as 7-8 times and can cause nusiance tripping on large inrushes. Square D makes a QOxxxHM for which trips at a more common 10x. Their QOxxxHID also can handle larger inrush currents.
 
Re: electrical ghosts

Originally posted by jim dungar: Available fault current has nothing to do with inrush currents.
Click to expand...
But it is not completely out of line to describe the initial moment of a motor's starting as being the same as applying a fault to the system. Until the motor starts moving, until it starts building up a "back emf," for the duration of the initial inrush, the power system is seeing a load consisting of wire, and only wire. That is what a fault is: a connection of phase to neutral (or phase to phase) with wire, and only wire.
 
Re: electrical ghosts

Charlie,
Of course an inrush looks like a fault current. But how does the available fault current of a transformer affect the amount of possible inrush current(that was mikesames point)?

Unless the power transformer is in a "power limiting" condition (i.e. core saturation) I would not consider it to be a typical method for limiting current.
 
Re: electrical ghosts

Originally posted by jim dungar:But how does the available fault current of a transformer affect the amount of possible inrush current?
Click to expand...
It is the upper bound of the current that could be supplied to the motor. The actual current will be lower, because of the resistance of the motor windings and branch circuit conductors. With the long extension cord, the current will be lower still. It is not an impossible answer, though I think it not the most likely.
 
Re: electrical ghosts

I wouldn't focus too much on the saw tripping the breaker. You could simply have a bad saw, and maybe the exten. cord does limit the fault current.

I had one case where the contractor said a breaker would trip every other time they started a motor. Turns out he just didn't leave time for the breaker to cool down before restarting the motor. There actually turned out to be a problem with the motor, but he got sidetracked by the breaker not tripping every single time.

Try other known loads, preferably a load bank or a outlet tester.

STeve
 
Re: electrical ghosts

Yes, the extension cord can limit the inrush current of the motor.

The amount of available fault current from a transformer has no impact on the inrush of a load, except if it cannot deliver enough. A larger than necessary available fault current does not increase the inrush drawn by a load.
 
Re: electrical ghosts

have you checked the quality of your ground ,where is the nuetral ground bond ?the panel you talked about ,is there a main service in the building ,breakers won't work properly if you have a bad ground .I would research this
 
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