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T8 LED Lamps - Direct Short? #942037
07/11/18 02:34 AM
07/11/18 02:34 AM
Joined: Aug 2013
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wirehead43 Offline OP
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wirehead43  Offline OP
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Joined: Aug 2013
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I'm replacing 48-inch T8 fluorescent lamps with T8 LED lamps. I've disconnected the ballasts and connected line power to one end of the LED lamps so marked. Works great. Out of curiosity I checked the two pins on the opposite end of the LED lamps and found they are actually joined internal to the lamps. So if someone inserts an LED lamp in the wrong direction it will be a direct line short that trips the breaker, fries some wiring or damages the lamp. Why would the lamps be configured this way or am I missing something? Seems that when replacing a lamp the average person would stand a 50:50 chance of getting it wrong.

Re: T8 LED Lamps - Direct Short? [Re: wirehead43] #942038
07/11/18 04:06 AM
07/11/18 04:06 AM
Joined: Sep 2003
Posts: 6,644
Jayhawk Land
RCovell Offline
Carpal Tunnel
RCovell  Offline
Carpal Tunnel

Joined: Sep 2003
Posts: 6,644
Jayhawk Land
I recently replaced my Church's yard sign fluorescent bulbs with LED equivalents. I daisy chained the hot on the bottom and neutral on top. The bulbs were marked with hot and neutral ends, so I could keep them straight. I also wrote a note with a Sharpie on the inside of the sign to alert the next guy, just in case.

Could your installation also use polarity specific bulbs?

Bob.

Re: T8 LED Lamps - Direct Short? [Re: wirehead43] #942048
07/11/18 11:25 AM
07/11/18 11:25 AM
Joined: Sep 2002
Posts: 9,841
Welland Ont. Canada
jdevlin Offline
Carpal Tunnel
jdevlin  Offline
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Joined: Sep 2002
Posts: 9,841
Welland Ont. Canada
Measure the other end and I bet you get the same reading.
There is probably a transformer on the input to drop the 120 AC to 2 v and convert it to DC. A transformer will measure as a short.

Re: T8 LED Lamps - Direct Short? [Re: wirehead43] #942053
07/11/18 01:57 PM
07/11/18 01:57 PM
Joined: Aug 2013
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wirehead43 Offline OP
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wirehead43  Offline OP
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Joined: Aug 2013
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Thanks for the suggestions.

On these bulbs the line connections (hot and neutral) both connect to the same end of the bulb marked as "LINE". There is no keying to prevent the bulbs from being installed in the opposite direction.

I didn't think to check if both ends of the bulb have the same resistance reading but will do so. But if both ends are the same, why would only one end be marked as "LINE" or even marked at all ??

Seems like a strange setup. Will let you know what I find.

Thanks again !

Re: T8 LED Lamps - Direct Short? [Re: wirehead43] #942057
07/11/18 03:41 PM
07/11/18 03:41 PM
Joined: Sep 2002
Posts: 9,841
Welland Ont. Canada
jdevlin Offline
Carpal Tunnel
jdevlin  Offline
Carpal Tunnel

Joined: Sep 2002
Posts: 9,841
Welland Ont. Canada
Post make and model of bulb or link so I can research online.

You could also try measuring from one end to the other to see if they are connected.

Re: T8 LED Lamps - Direct Short? [Re: wirehead43] #942080
07/11/18 08:26 PM
07/11/18 08:26 PM
Joined: Dec 2014
Posts: 792
Central Pennsylvania
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AnthraciteSparky Offline
Handyman
AnthraciteSparky  Offline
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Joined: Dec 2014
Posts: 792
Central Pennsylvania
Are the tombstones shunted or not ? I am in the process of converting a retro high school. It contains 22 apartments, a nursing school and a senior day care/ health center. As long as both LED tubes are inserted exactly alike we never have an issue. Even if you disregard the "L"&"N" they will illuminate properly.
Of course I am posting of ballast bypass LEDs, no practical reason to do otherwise. It is 2018.

Last edited by AnthraciteSparky; 07/11/18 09:01 PM. Reason: spelling

"Me, I'm just a lawnmower, you can tell me by the way I walk"

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