24 volt AC halogen machine tool lamp....do + and- wires matter ?

On a 24 volt Halogen lamp like this-

A-L11B IP65 Waterproof 7W Halogen Work Light w/ 17" Arm 24V Machine worklight | eBay

Does it matter which wire the + (from a control transformer labeled 0 and 24 on output side) is connected to on the lamp ? I suspect not, but making sure...


(now waiting for the first one to type "why mess with that when you could get a great LED lamp at IKEA for 99 cents"... )

The scoop in the linked ad indicates the input for the lamp is 24v AC which to me would indicate there is not a polarity issue.

Stuart

Many 24VAC control transformer circuits are not connected to a ground reference (one side grounded). But if it is, the grounded side or neutral should connect to the outside shell of the lamp-holder. Fixture doesn't appear to be marked in the ad which side is the shell.

SAF Ω

Why mess with that when you could get a great LED lamp at IKEA for 99 cents...

There, got that over with.

A halogen lamp is, electrically, no different from any incandescent lamp. So no, it doesn't matter to the LAMP. But it may matter to the FIXTURE if they bonded the secondary of that transformer to the frame itself. There does not appear to be a ground wire, which meant it would need to be "double insulated" in order to pass UL in this country. But this comes from Taiwan and does not appear to be UL listed, to you don't really know what liberties they took. It's PROBABLY OK, but not absolutely.

As I interpret that, YOU will have to supply it with 24VAC, that module is likely a rectifier / power supply to help it be safer around water by using DC for the lamp itself. Hard to tell without something nice like, oh, say, the installation instructions / manual?

24 volt doesn't need U/L. Only 48 volts and above.

Tom

Jraef said:

Why mess with that when you could get a great LED lamp at IKEA for 99 cents...

Click to expand...

LOL.....if only IKEA would copy Waldmann lamps.... still the end result of that might be like one of those current design Toyota FJ 40 "Africa Safari" type vehicles, which looks cool and tough on the outside but is more like a Hollywood set on wheels in reality.

SAF said:

Many 24VAC control transformer circuits are not connected to a ground reference (one side grounded). But if it is, the grounded side or neutral should connect to the outside shell of the lamp-holder. Fixture doesn't appear to be marked in the ad which side is the shell.

SAF Ω

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Please, never connect neutral to safety ground in any appliance. It will create a ground loop that can cause all kinds of strange noise related issues and it is against code.........everywhere! Neutral can only be connected to safety earth at the building entrance point. It is ok to connect a floating ac supply to neutral, but never ground.

steve-l said:

Please, never connect neutral to safety ground in any appliance. It will create a ground loop that can cause all kinds of strange noise related issues and it is against code.........everywhere! Neutral can only be connected to safety earth at the building entrance point. It is ok to connect a floating ac supply to neutral, but never ground.

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Not so in this case.

A transformer secondary is a "separately derived source", and in most power circuit circumstances is REQUIRED to be connected to the ground to re-establish a neutral for the circuit. NOT required for "double insulated" units, which are generally only low power transformers such as this might use..

Also not required if circuit is not accessible without a tool, and does not appear outside the equipment it is used in.

JST said:

Not so in this case.

A transformer secondary is a "separately derived source", and in most power circuit circumstances is REQUIRED to be connected to the ground to re-establish a neutral (and fault current return path) for the circuit. NOT required for "double insulated" units, which are generally only low power transformers such as this might use..

Click to expand...

II. System Grounding
250.20 Alternating-Current Systems to Be Grounded.
Alternating-current systems shall be grounded as provided for
in 250.20(A), (B), (C), or (D). Other systems shall be permitted
to be grounded. If such systems are grounded, they shall
comply with the applicable provisions of this article.

(A) Alternating-Current Systems of Less Than 50 Volts.
Alternating-current systems of less than 50 volts shall be
grounded under any of the following conditions:
(1) Where supplied by transformers, if the transformer supply
system exceeds 150 volts to ground
(2) Where supplied by transformers, if the transformer supply
system is ungrounded
(3) Where installed outside as overhead conductors

SAF Ω

Generally polarity does not matter for low voltage ac circuits such as lamps.

In the case of that particular lamp the wires appear identical in every aspect so I think it's mostly a matter of connecting them for the neatest wire dress. It should make no difference electrically.

Thanks folks. As an aside, it's interesting Eisen went up on the price $15 plus eliminated the free shipping since I ordered mine just a few days ago. My order must have triggered a "D'oh !" to whoever placed the ad.

They were lucky I also ordered the 120 volt version that did not have free shipping so at least they can ship both together and come out ok I suppose.

A-L11B IP65 Waterproof 7W Halogen Work Light w/ 17" Arm 24V Machine worklight | eBay

price was $75 and free shipping ! (cross country in this case...in fact over $27 just for the shipping now ! )

To the original point, you can just connect up the transformer either way, and can then either ground, or not ground the secondary. I'd ground it. I;d put an overcurrent protector on the transformer also, likely on the primary side. No reason not to, several reasons TO do it.


To SAF's point.........

The NEC covers "facility wiring". So those requirements actually apply to "branch circuits", circuits into which you will plug, or connect, arbitrary equipment in a facility with wiring running to various places in the building etc.

Within a machine, as in the case of machine lights, etc, the NEC does not reach, and there you have only to satisfy UL. UL makes the double insulation etc requirements.

So the branch circuit info is actually not applicable in this case, although it is good to remember it for general wiring, both for transformers, AND for backup generators etc. ANY source of power that has no direct wired "metallic" connection to the power company.

A transformer secondary has no direct connection to the power company, and so if supplying a branch circuit, SHOULD / MUST have a ground connection.

But this is off-topic.