Need to pick an electrical standards compliance/safety engineer/technician's brain

[TCJ]

Long story short:
Transformer in a PAR36 lamp fixture died. The lamp fixture had a 3-wire (grounded) power cord.
I scav'd a replacement transformer from some other equipment; it had a 2-wire (non-grounded) but polarized power cord.
The light fixture was approved by Ontario Hydro.
The appliance from which I got the replacement transformer was approved by CSA as "Audio Video Equipment".
The power supply module from which I yanked the transformer was approved by Underwriter's Laboratories as "Recognized Component".

Do I still need the 3-wire grounded power cord? Or can I get away with an ungrounded 2-wire?

 

[TCJ]

To clarify:
I do recognize that technically, the lamp fixture will lose its approval due to a power component being replaced with a different model. But what I'm asking is, politics aside, would the safety of the lamp be sufficiently compromised on an ungrounded power feed?

(Think of it as if the lamp was to hypothetically be submitted for evaluation and approval again, but with the new transformer. Would it still need the 3 wire cord to pass inspection? (Assuming nothing else wrong.))

Here's my thinking:
The lamp fixture has a metal enclosure. It's transformer was bolted directly to the enclosure. The HV isolation relied entirely upon the transformer's insulation quality.
The device from which I scav'd the replacement transformer had a metal & plastic enclosure. The transformer was bolted to a metal heat sink which was bolted to a metal part of the enclosure. Therefore the appliance is NOT a "double-insulated" class, and it too relies entirely upon the transformer's insulation quality.
The lamp's original transformer had paper insulation layers around its varnished "magnet wire".
The replacement transformer has its varnished "magnet wire" wound around a plastic bobbin with fairly large flanges, the bobbin then placed inside the magnetic core.

I'm guessing the plastic bobbin gives the replacement transformer a higher safety factor, which permitted the appliance to be approved even with an ungrounded power feed. Is my guess correct? (If so, I assume the lamp fixture could be considered equally safe now on an ungrounded cord, by using this "better" replacement transformer.)

 

[DuckJordan]

My question is why does the Par36 fixture even need a transformer? Is this a standard par fixture in which you replace the lamps or is this something different. What voltage in your space, and what is the voltage of the lamps.

Is there any reason you can't ground the fixture by screwing the ground wire to the housing?

 

[TCJ]

The lamp uses a 6V 30W spotlight bulb. The transformer steps down the 120V to 6V.

Of course I could ground the fixture... it has a ground lug inside riveted to the enclosure. But you have to admit, things with ungrounded cords -- especially if not polarized -- do offer more versatility / less hassle than things with polarized or grounded cords! So if I don't have to ground the thing anymore with the newer, better transformer... I won't.

...
I should also mention, the new transformer has an internal thermal fuse; the old one did not. And I decided to keep the fuse holder & fuse from the transformer donor appliance; the lamp fixture originally had no fuse protection.

 

[Chris15]

You need to earth the enclosure.
If the failure point is say the joint between incoming supply lead and transformer fly lead, then you have a live wire floating around shorting out to the casing.
At that stage the transformer's parameters are irrelevant. The human touching the casing becomes a grounding path for the supply lead.

 

[TCJ]

Just to be pedantic, the new transformer has solder studs on the bobbin flange -- no fly leads. And a small PCB soldered to the studs holds a typical glass cartridge fuse. The PCB has a pair of solder studs on it too, to which the other device's supply cord was directly soldered. Likewise, I'm going to solder the lamp fixture supply cord directly to these studs.

I am curious though, on what criteria did Ontario Hydro likely demand the light fixture to be grounded? And on what criteria did CSA permit the other device (from where I pulled the new tranformer) to remain ungrounded?

 

[TCJ]

Then again, I could just use the original grounded cord for the light fixture anyways, on the premise that "extra safety is never a bad thing".

(And then build a non-polarized ungrounded plug -to- floating-ground receptacle "cheater adapter" and toss it in my arsenal of "bad things"... if I ever desire powering the lamp from an ungrounded extension cord or ungrounded receptacle in old buildings. Shh, you didn't hear that. )

 

[STEVETERRY]

Then again, I could just use the original grounded cord for the light fixture anyways, on the premise that "extra safety is never a bad thing".

(And then build a non-polarized ungrounded plug -to- floating-ground receptacle "cheater adapter" and toss it in my arsenal of "bad things"... if I ever desire powering the lamp from an ungrounded extension cord or ungrounded receptacle in old buildings. Shh, you didn't hear that. )

This thread is making me very nervous for the following reasons:

1. The OP is largely answering his own questions.
2. No disrespect to the OP, BUT--The original question concerning the OP's desire to remove the grounding conductor on a listed luminaire due to the replacement of the transformer with one that is "better" clearly characterizes the OP's lack of knowledge to perform repairs or modifications to the luminaire in a safe manner.
3. Equipment grounding is not optional. It either is or isn't required by the original listing of the luminaire and it should never be changed. This is a life safety issue.

ST