I recently got a Crouse Hinds cobra head fixture. It was wired for 240volts (N.America) with just two wires; a black wire & red wire. There was no ground wire! The shell/common of the mogul socket had a green wire coming out (that's the only green wire anywhere and was tabbed with the white) & it was connected to the fixture. The diagrams are fairly easy to decipher, but in order to wire for 120volts with 3 wires (HOT/black + COM/white + GRN/ground), do I need to remove the green/shell wire?? Or is this needed for the CWI ballast? I believe it was there to keep the shell at 0v for the 120V - 0 - 120V wiring configuration in 240volt streetlighting that was used.

The only change is on the primary side (4 wires on 1 side of the ballast) - Rewire it as drawn in the label

Be carefull to really wire it exactly like that, and not swap any 2 wires, as this will result in a short circuit

The shell green wire is indeed to keep the shell at 0V, making use of the ballast as isolation transformer. But is it the only wire connected to the shell ? I would connect it directly to the other Earthed components, so that the working lamp current does not go through the lantern body

Ok but if if I use 120volts with green-ground wire, do I connect that also to the metal of the fixture??

The green wire connected with the lamp COM/shell, is also connected to capacitor & COM of ignitor!

The diagram shows only connection of the working circuit, not that much the protection.
As with any metal parts, all these should be connected to the PE (so the green or yellow/green wire from the mains input cable).

The shell should be then connected to that wire as well (to ensure there is no voltage on the shell; that is the main purpose of the SWI vs CWA). But be careful, the lamp current should never be able to flow through any wire between the PE connection and the lantern case (so if whatever connection get loose by a fault, it should not cause voltage on the fixture, nor ballast body).

Ok so I'll just reply without a pic but I'll link to my gallery.

Medved, I don't understand what you mean by "the PE connection"..PE? What is PE?

This is the actual ballast of the cobra head. Now wired for 120v. Previously, it had a black wire & a red wire at the block, for 240v (N.America). There was a sticker "wired for 240V" on the porcelain block which I removed. There was no green wire coming in!

And this is the Ballast.

Simple question(s): Do I connect the green wire from my 120v line to the aluminum fixture? And do I KEEP or REMOVE the green wire from the shell to the fixture with my 120v connection?

Ok so I'll just reply without a pic but I'll link to my gallery.

Medved, I don't understand what you mean by "the PE connection"..PE? What is PE?

It is an abbreviation of "Protection Earth", often called "Grounding" (although it does not necessarily mean a real ground connection). It uses to be the green, green/yellow (alternating stripes along the wire) or bare (not insulated) copper wire.
This conductor does never carry any normal load current. It's main and only purpose is to carry a fault current, when somewhere the insulation breaks, and so prevents dangerous voltage buildup between different accessible metal parts (even of different devices) and/or ground and in case that fault happens, ensures the circuit protection devices (GFCI or just regular circuit breakers or fuses, or in special installation even other type of devices) switch off the power into the affected branch.
So this wire interconnects all the accessible metal parts (metal body, cover, structures,...) together and to a grounding electrode (in insulated networks it could be just an interconnection, but these systems you won't find in homes; in some older installation it is grounded via a sensing coil of the main protector, but that system is no longer used in any new installations).


Some newer devices (mainly power supplies of many IT devices or so), whose won't need the PE for safety reasons (as they use double/reinforced insulation construction anyway), use this conductor only to connect an EMC shield and to carry out the leakage currents from the RF suppression capacitors (those leakages are usually safe for humans, but the charge of the RF suppression capacitors could be deadly for the sensitive electronic), so the PE interconnection gets an extra, non safety related function as well.

This is the actual ballast of the cobra head. Now wired for 120v. Previously, it had a black wire & a red wire at the block, for 240v (N.America). There was a sticker "wired for 240V" on the porcelain block which I removed. There was no green wire coming in!

And this is the Ballast.

Simple question(s): Do I connect the green wire from my 120v line to the aluminum fixture? And do I KEEP or REMOVE the green wire from the shell to the fixture with my 120v connection?

Yes, the green wire is connection of the PE, so it has to be connected to the fixture body and preferably to the ballast core as well (as the ballast is the "prominent" component, where the fault is most likely to happen).

Interesting isolating ballast--for 240V the primary windings are strapped or connected in series-for 120V they are connected in parallel.The isolating ballasts I have are for one voltage only.Have two for 120V 250W and another 400W HPS lamps.I have a GE 150W isolating ballast fixture for 480V.Thinking of looking in my junkbox and see if I have a TV transformer that I could power the ballast off its HV winding-may work.the fixture uses a 150w mogul base HPS S55 lamp.Would like to run this light-got it as surplus from ECU.

This is quite common arrangement for most equipments with a transformer on the input. It is the only method utilizing all the winding all the time, so not needing an oversized winding (if you use taps, the 120V section has to be rated so to handle full power, but still the extra winding for higher voltages has to fit; when used at higher voltage, the 120V section is used only at low current).

Thanks for all the help! Here it is. This was my first CWI ballast. I had never seen the socket-shell grounded before! This ballast is extremely silent. I can barely hear a high-pitched sound. The head also had my first ever short-cap in the place of the photocontrol. 3 wires went to unconnected tabs onto the block. If there was an actual PC then I'd be even more confused.