Hi,
I have a Japanese movie projector that I presume was designed for use in a 110v neutral ground set up , as there is no earth wire inside it .

I’ve had to replace the projectors power input socket as it came without a power lead and despite searching high and low , I couldn’t find a plug for it . I replaced it with a five pin aeronautical type connector . I’ve used three of the pins for L N and E . Since there was no original earth in the machine , I’ve added an earth myself to the chassis . I’ve connected this earth , via the cable to the fat ground pin of the cee form plug at the other end of the cable . This plugs into a standard power tool type 110 step down transformer. My questions are , is this the correct way to ground the machine and are the 110 outputs of the transformer designed for direct ground or neutral ground ? I’m assuming as it’s UK , it will be direct and my chassis ground should work ? . Just want to check and any help will be greatly appreciated. Jon

 

Hi,
I have a Japanese movie projector that I presume was designed for use in a 110v neutral ground set up , as there is no earth wire inside it .

I’ve had to replace the projectors power input socket as it came without a power lead and despite searching high and low , I couldn’t find a plug for it . I replaced it with a five pin aeronautical type connector . I’ve used three of the pins for L N and E . Since there was no original earth in the machine , I’ve added an earth myself to the chassis . I’ve connected this earth , via the cable to the fat ground pin of the cee form plug at the other end of the cable . This plugs into a standard power tool type 110 step down transformer. My questions are , is this the correct way to ground the machine and are the 110 outputs of the transformer designed for direct ground or neutral ground ? I’m assuming as it’s UK , it will be direct and my chassis ground should work ? . Just want to check and any help will be greatly appreciated. Jon

A power tool transformer is wired with its centre tap earthed, so you actually have two 55V live conductors, 180° out of phase.
If neither of the two power conductors which you have called Live and Neutral connects to the chassis, then you have it correct.
If neutral connects to the chassis, don't use it.
If it will pass a flash test of 2kV between Live and Chassis, and between Neutral and Chassis, then it is double insulated, and you need not connect the chassis to earth.

Note that the mains voltage in Japan is 100V, so make sure that the lamp is suitable.
A 100V lamp on a 110V supply will have very poor life.

 

Thanks for that . I’ve replaced the lamp with a 230 v . So just so I know I’ve got it right , the two outputs (110v) from the secondary on the transformer both have the larger pins of the sockets wired to earth so in turn via my cable they will go to my earth chassis? Thanks , Jon

 

Thanks for that . I’ve replaced the lamp with a 230 v . So just so I know I’ve got it right , the two outputs (110v) from the secondary on the transformer both have the larger pins of the sockets wired to earth so in turn via my cable they will go to my earth chassis? Thanks , Jon

Why a 230V lamp? You only have 110V from a power-tool transformer.

 

The lamp house is a bolt on so I’ve fitted a separate 230 supply to it . 100 v lamps are hard to come by here

 

First, that third wire, "earth ground" is not an operational requirement, it is for reducing the shock hazard in the event of an internal isolation fault in a device.
As for the "power tool step-down transformer, I suggest doing a resistance check with it volt connected to any power. Having any portion of a portable tool power tied to " frame ground" seems like an open invitation to some real excitement, electrically speaking.

 

Thanks for your reply.

The earth wire is attached to the chassis and then (via the cable,) to the ground pin of the transformer output socket . Would this not be a direct connection to earth and therefore an extra safety precaution or is it potentially hazardous? I realise that the transformer centre tap is effectively behaving like a neutral ground and should provide good protection, I’ve added the earth just to be extra safe (I hope !)

 

The "green wire ground" added will not be a hazard if done as you describe. It is an added expense safety feature to protect folks from a hazard that seldom occurs, which is an internal short circuit to the frame in an appliance. AND it only provides any potential benefit when there is a grounded source that a person could contact while also contacting the appliance with the internal short circuit. So how many grounded water pipes do most folks have in their living room, the library, or their bedroom???

 

If it required contact with a metal object to get a shock, then no-one could ever get a single-point-of contact shock.
The earth wire also makes sure that the body of the power tool does not float to a higher potential due to capacitive coupling through the transformer.
Most power tools these days are double insulated, so the earth is rarely connected, but the transformer's earth connection ensures that no part of the power tool is ever more than 55V from ground. Enough for a shock on a rainy building site, but rarely enough to kill.
So, if the appliance is double insulated, then ignore the ground connection.