Thread: Powerfeed transformer wiring diagram

So did you get your money back?

Stuart

Originally Posted by elkangorito

The fact that you have identified the transformer as being 'crook' is a good thing.

With regard to the wiring of the new transformer, you MUST NOT connect any part of the 'Secondary Winding' to earth.

An earth wire/cable MUST be connected to the metal chassis of the transformer enclosure. This wire/cable MUST come from your switchboard (consumer unit).

There MUST NOT be any other earth cables, with the exception of below;

With regard to your load, other eath cables are connected as 'equipotential earth conductors'.

Hi Elkangorito,

Agreed, the wiring standards for a transformer isolated supply are clear on that point, the secondary windings have no voltage with respect to earth. But as you know, many machines imported into Australia don't meet the standards, here is the wiring diagram of the HM52 mill, I have highlighted the earth connections in colour, the green is what I believe to be correct protective earth connections. The red slashes are where I believe the connection should be broken. The blue lines are the isolated return lines from the 24v and 110v transformer secondary windings.



The manufacturer has just connected all the earths and the secondary "neutrals" back to mains earth...

Hope you can make sense of it. Am I correct with the modifications required to meet the standards?

Regards
Ray

RayG
As you know I'm no expert. But,
If you move the lower red wire cut to where I have put a yellow line. Doesn't remove the potential to earth yet still allow the chassis to be earthed?

Stuart

p.s. looking at it again, why do you even need the second cut? Isn't the first cut enough?
I think I might be about to learn something new

I hope someone tells one of the world's biggest computer manufacturers about this too. It seems that some laptop power supplies also earth one of the output pins.

Maybe they're wrong - but I doubt it. Their products carry approval symbols from all over the world.

My transformer is wired up the same with earth wires connected to the 0 pin on the secondary side of the transformer

Hi Stuart,

I see what you mean, but my understanding is that the transformer frame must be grounded, so that any fault on the primary windings to ground should generate fault currents which trip the RCD circuits.
This is different to the secondary windings where a fault to ground won't generate any faults leading to the RCD trip. Whether you earth it or not.

I hope someone tells one of the world's biggest computer manufacturers about this too. It seems that some laptop power supplies also earth one of the output pins.

Maybe they're wrong - but I doubt it. Their products carry approval symbols from all over the world.

Interesting, I have noticed that also, the ones with 3 pin plugs seem to carry the earth through to the DC ground.

I would believe that they meet the relevant standards, so maybe, the compliance is something to do with double insulation?

EDIT: I just checked a couple, and the ones with the dc ground connected to mains ground don't have the double square symbol. So I guess they aren't double insulated. The toshiba one with just two pin mains is of course double insulated and has the double square logo...


As to why they do it, I guess it's to do with EMI, or maybe grounding issues with external equipment like monitors, printers etc..

There are plenty of double insulated laptop power supplies with just the active/neutral connection, and no ground.

I recall a case years ago where a guy at the local tafe college imported computers direct from taiwan, one of the moulded iec power cables had neutral / earth reversed. Wasn't a problem he noticed, until he plugged it into an incorrectly wired power point which had active/neutral reversed. The path to ground was through the computer cpu board to the monitor. Lit up like a christmas tree with popping sound effects to match...

Regards
Ray

Originally Posted by RayG

Hi Stuart,

I see what you mean, but my understanding is that the transformer frame must be grounded, so that any fault on the primary windings to ground should generate fault currents which trip the RCD circuits.
This is different to the secondary windings where a fault to ground won't generate any faults leading to the RCD trip. Whether you earth it or not.

Ray I agree about the transformer frame needing earthing. But once you have removed the link between the transformer frame and the secondary winding you have isolated the secondary, why then try to isolate the earth of the power feed and DRO? I agree there isnt much point earthing them in relation to the secondary of transformer, but I think earthing them might help if there is a fault in some other piece of equipment.(whould it help with static?)


.RC.
Mine isn't earthed. The E termail isn't lol

Stuart

Originally Posted by Stustoys

Ray I agree about the transformer frame needing earthing. But once you have removed the link between the transformer frame and the secondary winding you have isolated the secondary, why then try to isolate the earth of the power feed and DRO? I agree there isnt much point earthing them in relation to the secondary of transformer, but I think earthing them might help if there is a fault in some other piece of equipment.(whould it help with static?)


.RC.
Mine isn't earthed. The E termail isn't lol

Stuart

Hi Stuart,

I think that's pretty much where I get to, with this whole question, if there is no voltage with respect to earth on the secondary side, it won't make any difference.....

It might in fact be difficult to isolate that connection without insulating the mounting, the power feed and dro are both mounted direct to the machine frame, which is earthed anyway. I must check to see if there is a seperate earth wire from the power feed. I know it's shown as a seperate wire on the circuit, but it could just be connected to the frame.

Regards
Ray

Originally Posted by RayG

IEDIT: I just checked a couple, and the ones with the dc ground connected to mains ground don't have the double square symbol. So I guess they aren't double insulated.

I understand that it is "Class III" earthed. It is a new standard - and it has a new symbol (but the symbol is not in common usage yet).

Originally Posted by RayG

Hi Stuart,

I think that's pretty much where I get to, with this whole question, if there is no voltage with respect to earth on the secondary side, it won't make any difference.....

Agreed, but you "could" get voltage from somewhere else, say a faulty extension lead. If you had managed to isolate the DRO from earth it may now be live(but if you want to get that excited any piece of angle iron laying on the floor could have the same problem and with luck the RCD will work)

.RC.
Just out of interest I've just checked my mill. its secondary is isolated and neither of the earth pins on the two 110V sockets is connected.

Stuart

Originally Posted by steran50

In Australia a lot of Auto Electricians Work on Fridges, Freezers, Electric Motors, Power Tools, Welders etc and in that sense, they do need to know something about Domestic and Industrial Electrics.

Are these guys qualified to work on high voltage appliance wiring?..they need to hold the appropriate licence...i suspect that a auto elec having a licence for high voltage appliances would be very rare

so which is it...to earth the 110v side or not

my trany has an earth from the chasis to the earth link.

the 0V side of both the 110v & 24V side are bridged and connected to earth.

the chasis from all accessories should have a connection to earth if I am not mistaken

Just rang a switchboard making sparky who said the secondary side can be done two ways
1. A double pole circuit breaker on both legs of the secndary and no earth from the 0v connection
or
2 A circuit breaker/fuse on the secondary side and the other side ie the neutral is earthed

Originally Posted by RayG

MM just checked the wiring diag for my HM52 and it doesnt show any fuse or the like for the 110v secondary side like yours does Ray...maybe i'd better fit something

Hi eskimo
The answer seems to be "depends who wired the machine".
My opinion for my machines is that it would do more harm than good.

Got a picture?

Stuart