The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Sprinklered equipment 26-008
by bigpapa
12/02/16 04:24 PM
On Delay Relay with Auto Reset
by Potseal
12/01/16 09:59 AM
Wow, that was close!
by jraef
11/28/16 07:06 PM
Earthquake in New Zeeland
by RODALCO
11/27/16 11:25 PM
Calling all Non-US members!! (Non-US only)
by Tjia1981
11/27/16 06:33 AM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
gfretwell 14
HotLine1 10
Trumpy 8
Texas_Ranger 8
sparkyinak 7
Who's Online
0 registered (), 214 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#46773 - 01/02/05 03:48 PM Low voltage x-former problem?
Northbayec Offline
Member

Registered: 12/16/04
Posts: 26
Loc: San Rafael, CA U.S.A
Hello everyone and happy New Year!

I had a problem with a some site lighting at a residence a couple days ago where the owner said he could not get half of his walkway lights to work. It is a 12 volt system and when I check them out 3 of them are working but the other 7 are not. I figure there is a bad splice so I re-splice a 3-way connection after the 3 light (the farthest one from the x-former that worked) and when I turn them on I get 12 v at the connection for the next light but when I hook that light up the votage drops down to zero at that connection but the first three lights are still working. There were ten 25watt fixtures on a 250 watt x-former so I am assuming that I need to replace the x-former but I don't see an explaination on the voltage differences on the same system. Anyone out there have any input on this.

Thank you
John

Top
Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#46774 - 01/02/05 05:57 PM Re: Low voltage x-former problem?
dereckbc Offline
Member

Registered: 10/08/03
Posts: 158
Loc: Tulsa, OK
John, the transformer is not the problem. You still have a continuity problem between the 3rd and 4th light. You are seeing high resistance, so you see 12 volts with no load but 0 when load is applied. Sounds like it is time to dig things up and find the bad connection.

Top
#46775 - 01/02/05 07:03 PM Re: Low voltage x-former problem?
Wirenuttt Offline
Member

Registered: 11/10/02
Posts: 267
Loc: Massachusetts
Also some of these LV lighting systems transformers are designed to run no lower than 50% and no higher than 80% of computed light load.

Top
#46776 - 01/02/05 10:54 PM Re: Low voltage x-former problem?
Physis Offline
Member

Registered: 12/28/04
Posts: 85
Loc: Burlingame, Ca. USA
I did an installation where the owner called me back a couple of monthes later because half of one of the branches were not lighting (I think he thought I didn't do it right). I went for the wire after the last working light and snipped out the piece where the gardener's shovel got a little too close. He wanted that to show to the gardener.
_________________________
Sam, San Francisco Bay Area

Top
#46777 - 01/03/05 12:55 AM Re: Low voltage x-former problem?
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
John,
What you have is a Dead-Short in the 4th fitting.
It sounds to me like these lights are in Parallel, not Series.
The short is preventing any current flow to the other fittings further down the track.
If the guy keeps running the system like that he will need a new transformer.

{Message edited to add last bit}

[This message has been edited by Trumpy (edited 01-03-2005).]
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

Top
#46778 - 01/03/05 06:00 AM Re: Low voltage x-former problem?
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
 Quote:
What you have is a Dead-Short in the 4th fitting.

Mike,
How do you figure that? If there was a dead short the other lights would go out.

I go with Dereck's answer: There is a bad (high-resistance) connection somewhere. When you just put the meter at the 4th lamp terminals it's drawing very little current, so you see the 12 volts. As soon as you connect the low-resistance of the lamp, the high-resistance of the bad connection becomes the dominant part of the circuit, so the voltage at the lamp drops to zero (or very nearly so).

Top



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals