Earthing toroidals?

[Daemon]

Hi all

We use the multiple earthed neutral (MEN) system here in New Zealand.

Everything wired to the house has a phase, neutral and earth wire except for double insulated appliances which only have the phase and nuetral.

How do I tell if my toroidal transformer is double insulated or not? Or failing that is it possible to safely earth it as it doesn't have an earth wire going to the primary, and how would I do that?

I am going with the option of running the 230v out to the ssrs boxes outside which house the transformers so I need to make sure that anyone in the vicinity of the transformers power connection will be safe.

Thanks again

[polar bear]

G'day, here is my two bobs worth: double insulation comprises both basic insulation AND supplementary insulation. you should earth the frame and any exposed parts ( not the terminals ) that may become assesable to any prying finger . The M E N system means that the earth and neutral wires are bonded to each other in the meter box so that the neutral and earth wire are at the same potential. there should also be a earth stake close to your meter box. hope this helps.

[jgrei1]

the toroid itself doesnt neccessarily need earthing but most people do earth the steel clamp for safety. if its in a steel enclosure i would definitely recommend earthing that.

[Daemon]

It will be in an abs ip67 rated plastic enclosure. What metal clamp are you referring to?
The only metal in the enclosure will be the mounting bolt through the centre of the toroidal.

The electrical cord run out to the enclosure will be plugged into an rcd anyway so would that be safe enough?

[MikeUK]

Many toroidal transformers sold in the UK these days are sealed in a container filled with potting compound. By definition, this type is double insulated. The earlier designs were supplied with two large steel washers the same outer diameter as the transformer and a bolt to clamp the transformer to the chassis. If you wanted to safety earth this type, simply attach the earth wire to the bolt. In the event that the transformer insulation breaks down your RCD will trip before anything nasty happens.

[jgrei1]

It will be in an abs ip67 rated plastic enclosure. What metal clamp are you referring to?
The only metal in the enclosure will be the mounting bolt through the centre of the toroidal.

The electrical cord run out to the enclosure will be plugged into an rcd anyway so would that be safe enough?


the steel washer that clamps the toroidial down. plastic encolsure will be classed as double insulated. so no earth is required if any of the loads do not require one.

if you have any more questions it is probably quite advisable to ask an electrician. even if it costs you a couple of dollars. liability in australia is a huge factor regarding these things nowdays.

regards, jeremy

[Daemon]

Hi

I am sort of getting too messages here now. One that the plastic container will make it classed as double insulated plus another that is saying I could earth the bolt that mounts the toroidal to the plastic container.

I am more than happy to earth the bolt. Just wanted to make sure it was a) neccessary or advised and b) safe to do so.

I hereby release you all from any and all responsibility and liability.

Thanks :)
Steve

[prof]

It has been posted previously in another toroid thread that only one side of the mounting bolt is to be earthed. The bolt will act as a short circuited winding if both ends of the bolt are electrically linked together.

[Daemon]

It has been posted previously in another toroid thread that only one side of the mounting bolt is to be earthed. The bolt will act as a short circuited winding if both ends of the bolt are electrically linked together.

Thanks Prof

Only an issue if both sides of the bolt are touching metal though right?

[Matt_Edwards]

You have to break through the insulation. The top disk/washer assembly can't touch any other steel parts other than the mounting bolt. then you will be fine.
KR
M

[Daemon]

Thanks