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#69995 - 09/27/06 09:00 PM Finding hots associated w/common neutrals  
jfwayer  Offline
Member
Joined: May 2005
Posts: 30
Fairmont, WV, USA
I'm working for a school system with 20+ buildings of various ages from 100 to 0 years. Many of the fuse and panel boards are not marked or incorrectly marked. We've been having trouble adding outlets and lights to circuits with shared neutrals in 120/240, 120/208, and 277/480 configurations. I'm looking for a method to determine the origin of a circuit and the other hot wires associated with the shared neutral. Are there any trick ways.

My current idea is to make a flashing load of several amps, connect it to the circut. Then go back to the expected panel board and look for wires that amprobe at the flashing rate. This should id the hot and neutral for the target circuit. Then I grub in the panel board for other hots associated with neutral. AssUme'ing no one's tapped a random neutral wire in a junction, I've found the hots and neutral.

I'd like much easier way... if it exists.

Thanks,

Jim Williams


JFW

Work Gear for Electricians and the Trades

#69996 - 09/28/06 07:15 AM Re: Finding hots associated w/common neutrals  
jkraft  Offline
Member
Joined: May 2003
Posts: 74
What do you use for the flashing load?


#69997 - 09/28/06 07:42 AM Re: Finding hots associated w/common neutrals  
Tiger  Offline
Member
Joined: May 2005
Posts: 706
Crystal Lake, IL USA
That sounds like the easiest way to me. You can do this hot. Otherwise you might disconnect the wires & do continuity tests, but that won't be quicker.

Dave


#69998 - 09/28/06 08:14 AM Re: Finding hots associated w/common neutrals  
SteveFehr  Offline
Member
Joined: Mar 2005
Posts: 1,205
Chesapeake, VA
There are cable clamp signal generators made specifically for this- you clamp them at one end and walk along with a trace probe which can track them through walls. We use them all the time for tracking data cables; I've never personally used one for power cables, but I've seen them, our one meter had clamp attachments for it and probes for finding leakage from broken underground cables too. There is some issue with bleed-over to other nearby circuits when it branches out, but the signal is always attenuated on the other cables, and strongest on the one you're tracking.

If you know where the cable end points are, your solution sounds easiest. In fact, I did the exact same thing last week- used a small microwave (manually) pulsed on and off to verify which circuit breaker was feeding the string. A 10A pulse is hard to mistake!

[This message has been edited by SteveFehr (edited 09-28-2006).]


#69999 - 09/28/06 09:42 AM Re: Finding hots associated w/common neutrals  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
A flashing load is made by getting one of those old-fashioned "buttons", and inserting it in the socket under the bulb. They were once common for Xmas displays- and are still available. They are limited to 60 amp loads.

The problem with using several at once is that there is no way to have them trip in time with each other.

Still, the 1/2 amp fluctuation is useful in finding circuits.

I have also found the usual circuit toners to be useful in finding the appropriate neutral in the panel.

Adding a large load, as with a space heater, might also help find the right wire.


#70000 - 09/28/06 02:37 PM Re: Finding hots associated w/common neutrals  
mxslick  Offline
Member
Joined: Oct 2004
Posts: 803
Atomic City, ID USA
Quote
They are limited to 60 amp loads.


That'd be one heck of a large button flasher..for mogul base sockets, right? [Linked Image]

I'm just gonna take a stab-lok here, you really meant 60 watt? [Linked Image]


Stupid should be painful.

#70001 - 09/28/06 03:30 PM Re: Finding hots associated w/common neutrals  
wa2ise  Offline
Member
Joined: Nov 2002
Posts: 782
Oradell NJ USA
Quote
That'd be one heck of a large button flasher..for mogul base sockets, right? :-)


Maybe that flasher is what is used to drive those broadcast transmitter towers flashing red lights? [Linked Image]


#70002 - 09/28/06 07:08 PM Re: Finding hots associated w/common neutrals  
renosteinke  Offline
Cat Servant
Member
Joined: Jan 2005
Posts: 5,316
Blue Collar Country
MX... I sure did mean 60 WATT! I'd go back and edit, but then, everyone would be confused by your post.

OOPS!

Guys, my e-mail is in my profile. I make a stupid goof like this again... and Mr. Murphy says I will... how about just dropping me a line?


#70003 - 09/29/06 03:24 AM Re: Finding hots associated w/common neutrals  
skipr  Offline
Member
Joined: Jan 2005
Posts: 39
Huntington Beach, Ca.
seems like a Amprobe AT-2004 advanced tracer should do just fine.


#70004 - 09/29/06 07:27 AM Re: Finding hots associated w/common neutrals  
32VAC  Offline
Member
Joined: Jun 2004
Posts: 202
Alice Springs, NT, Australia
I use a 1200 watt bar heater which gives me 5.1 amps @ 230 volts. Put the clamp meter on the circuit, take a reading, switch the heater on, if it goes up 5.1 amps, you're on the right circuit.


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