Made a service call. Connect up a large screen TV. Extended the cable (coax) to the sets location. Hooked the cable to the cable box. Pluged in both the TV (3wire cord) and the cable box (2wire cord) I then connected the RCA video & audio cables to the back of the cable box and my helper plugged the rca cables in to the monitor and spark and smoke came out of the cable box. The RCA cable melted. I quickly pulled the plugs. I connected the TV an measured 120v between the cable box (shield) and the TV chassis. Both cable box and TV were plug into a Isolated Ground receptacle. The building was a bank and is now a coffee house. I checked the outlet and found 120v between the ground prong (hole) and the cable shield, and between the ground prong (hole) and the box. I found the breaker controlling the ckt. and turned it off. All voltages gone. Removed the outlet, found it was served by 12/3 bx with BK/WH/RD with the RD connected to the IG ground terminal. Someone had connected this red wire to the hot line in the J box in the ceiling. I removed the hot and installed a propery wired receptacle. The band members has been using this receptacle for their equipment and complained about hum. The fact that all their equipment was electricly hot, it is a wonder someone did not get electrocuted. Always use caution with IG receptacles. Robert
Unfortunatly. having worked as a commercial sound technician for many years, the FIRST thing many people do when there system hums is yank the grounding pin. Audio signals (TRS & XLR connectors) are usually tied in with the electrical ground of the sound system. This creates a loop, which can cause a hum. The proper way to get rid of a hum is to transformer isolate the audio line, or ground lift the audio line itself. Leave the electrical connection alone. Sorry. This has always been a rant of mine.
As for the outlet in the bank/shop, isolated ground outlets are nice when wired right. Whoever used a red wire as hot should be shot. People like me get sent to the hospital because of stunts like that.
I know we talked about reidentifying the red as a ground before. As far as I know there is no problem with that as long as it's reidentified at BOTH ENDS. This was not the case here and apparently someone came along and assumed the red was a hot.
They do make IG MC cable, it has two grounds- one green and the other (IG)yellow/green. You don't need to go as far as HCFC cable.
[This message has been edited by hbiss (edited 11-22-2006).]
Smokeumchevy: Ya I have seen the red as an IG many times before as well, BUT now if thats the case the inspector will not even pass it if its taped green, you MUST re-identify the red with GREEN heat shrink tubing.
BTW where in Ontario are you? Just wondering as I am in "The Hammer".
In Victoria we used to allow the red wire in BX to be taped green for IG outlets. Since ISO bx has become redily available we will no longer permit green tape on a red wire. Red is not a good color for a bonding conductor and this illustrates the reason.
Another question that comes to mind is where did the original installer intend to land that IG in the box? It's supposed to go back to the service ground bar. Ground it to the box and you don't have an IG and you are wasting your time with an IG receptacle.
That is if you aren't wasting yout time with an IG anyway...