3phase motor question

[iwire]

He said the motor would immediately trip the breaker so he was probably taking the unloaded voltage. You're measuring voltage with a 10,000kohm load when you use a multimeter which makes it prone to picking up ghost voltage. 6W holiday incandescent lamp will draw 0.05A or has an impedance of 2.4kohm when lit up. This draws 4,000 times more amps from the circuit than a multimeteIt does exactly the same thing LoZ does. The affected leg won't light up or will be dim or flicker. If it does manage to light up normally without the motor connected, the affected leg will drop out when it is repeated with the motor present.

Filament light bulb is a PTC that has about a 10:1 ratio and it's a simple but a useful instrument because it responds quickly to power glitches. Usually the very first power related issue is flicker. Industrial motor circuits don't share power with lights but when you hook up a power quality meter and press "flicker" it will let you see the same thing you see by hooking up three light bulbs, but they can still have issues with phantom voltage.

Power quality meter is more convenient to hookup and can capture something that happens when you're not there. You certainly won't have to rig up 12v controls transformers connected to some brake lamps nor do you have to worry about those hot light bulbs burning you.

A lot of typing, little result.

 

[ActionDave]

The light bulb that sips power off through the bad connection would lose power/flicker and you can see all three phases side by side which is not possible with a clamp meter/dmm.

I knew there was a bad connection sitting on my couch and advised the op to find the weak link in the wiring without any Christmas lights, so did at least a half dozen others that participated. Physically tracing out the circuit and talking to someone on site is what solved the problem.

 

[growler]

He said yea they moved that fan outside because it was too loud and would rattle through the office area suspended ceiling. Well after crawling back into this old storage loft there mounted on the inside of the exterior wall my missing disconnect. 3ph 30 non fusible service disconnect. Open it up and to my delight was burned up leg number one. Intermittent problem that might never have been found if the installer didn't run out of black thhn that day. Plus too lazy to move said disconnect outside where it belongs.

I had a similar problem with a sign. Sign was high up on the exterior of a hotel. Sign company says they have no power. I check it out and find that power is good feeding the sign(disconnect switches on inside of wall ). Again the sign company comes back and says they have no power.

I think they are a bit off so I tell them if they will just schedule a time I will meet them and prove there is power to the sign. Turns out they have been checking for power at the exterior disconnect switch mounted on the sign and not finding any power. The disconnect switch had been bypassed (by the sign company) some time ago and they would never get power there because it went directly to the sign.

Once people rig things they are just asking for trouble at some point.