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Discussion Starter · #1 ·
I got a call from a building engineer asking me to diagnose an exhaust hood. Apparently there had been some demo and the workers before cut off the pipe coming out of the switch and pilot light.

I opened the old junction box and was surprised to find a brown, orange, yellow. 480 colors. I turned on and got 120 across the board. Okay so it's not 480.

I then took off the pilot/indicator light and the switch too. The orange hit pilot and then the switch, out the other side of the switch came the yellow and then hit the other side of the pilot light. To me this is a dead short but engineer said it was never touched and used to work.

I wasn't able to gain access to the penthouse where the starter is but how can I get 120 off both wires and not have it be a dead short.

I'm looking for a jump start before I get back in tomorrow. Thanks guys.
 

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animal lover /rat bastard
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13,547 Posts
yellow to yellow
orange to orange
brown to brown
gray to gray
 

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Donuts > Fried Eggs
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What was the potential between the yellow and orange?

My guess right now is that it's a 240V or 208V 1Ø exhaust fan and they controlled it only by switching a single leg. You're reading the second leg backfeeding through the motor winding.

What did you use to measure voltage?
 

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Discussion Starter · #4 ·
I should have typed that better. Brown was zero, orange was 133 volts, and yellow was zero.

I figured the hot (orange) would come from starter hit the switch and when turned on would fire up the coil (yellow) starting the fan. I then figured brown was the neutral coming off the pilot light.

To my surprise the orange hit the pilot then the switch which is my 120. The yellow came out the switch and then hit the pilot light.

Facts so far- pilot had no neutral. Pilot light has dead short(to me at least). Orange has 133v. Brown and yellow have zero. Orange and yellow come out of pipe that was cut. Brown was just left in box.
 

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Donuts > Fried Eggs
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The pilot light isn't gonna create a dead short, it's just a load. Though it almost sounds like it lights up when the motor is off, which would be a weird setup.

Sounds like they just used orange and yellow as a switch loop. Orange, constant hot. Yellow, switched conductor to your load.
 

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Discussion Starter · #6 ·
So your saying the pilot will work with the return going back to the coil of the starter. In other words the coil would act as a neutral for the light and the power to pull the starter.
 

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Donuts > Fried Eggs
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That's what it sounds like to me. When you close the switch there's no potential between orange and yellow, so the light stays off, however there is voltage drop across the coil so the contactor pulls in.

Open the switch and the coil conducts enough current to neutral to allow the pilot light to illuminate, but the light can't pass enough current to pull in the contactor so the fan doesn't come on.

Not how I would wire it, but it would work.
 
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