One of my power transformers developed a short - firsthand knowledge of how important is a good ground!
Since I had a bit of mechanical hum from the old ones, I want to mount them on a rubber pad. I installed grommets in the mounting holes and was planning on using some rubber washers under the bolts to help with eliminating the hum. The hum is purely mechanical and the transformers have a history of this. As a matter of fact, the company sells a rubber sheet specifically for this purpose.
So how can I safely rubber mount these transformers while insuring a safe electrical ground? I was thinking of running a wire from one of the mounting bolts to the chassis. Does that fulfill safety requirements? The end-bells bolts are insulated with plastic shoulder washers and cardboard sleeves so electrically seem isolated from each other. Should I use one wire from each end-bell mounting bolt to the chassis?
Thanks for any help
Dave
Since I had a bit of mechanical hum from the old ones, I want to mount them on a rubber pad. I installed grommets in the mounting holes and was planning on using some rubber washers under the bolts to help with eliminating the hum. The hum is purely mechanical and the transformers have a history of this. As a matter of fact, the company sells a rubber sheet specifically for this purpose.
So how can I safely rubber mount these transformers while insuring a safe electrical ground? I was thinking of running a wire from one of the mounting bolts to the chassis. Does that fulfill safety requirements? The end-bells bolts are insulated with plastic shoulder washers and cardboard sleeves so electrically seem isolated from each other. Should I use one wire from each end-bell mounting bolt to the chassis?
Thanks for any help
Dave
I would use a thick wire from the transformer directly to ground (chassis). Make the wire as short as possible and make sure you connect to the bare metal of the transformer (and not have a layer of laquer on the surface). Measure the resistance betweeen transformer and ground, it should be ZERO Ohms.
Regards, Gerrit
Regards, Gerrit
I use a mounting screw of the transformer to bond the FG/earth (greewn wire) from the AC plug. That away the GCFI on the household power trips that, but technically, if your secondaries have a ground path, they will provide enough protection for the other side of the transformer. Rarely I've seen the body of a transformer be energized by its short. But me and UL labs settled on this transformer tab grounding scheme a long time ago as the best approach.
The hum might be from over voltage which can be fixed in a couple of ways. This would be one of them:
If you add a ground wire from each end bell to the chassis, scrape off the paint on the bell
underneath the bolt for good electrical contact.
underneath the bolt for good electrical contact.
Gotta do the same thing on anodized sheet metal also.
Except on custom made chassis parts, when the anodizer can put a sticker over the area
around the hole, to keep it bare when in the bath.
Except on custom made chassis parts, when the anodizer can put a sticker over the area
around the hole, to keep it bare when in the bath.
A concern is that the core remains floating - even if both bell-ends are adequately linked to chassis - depending on how the core clamping is achieved. If a core clamp rod is insulated from the core by eg. end fibre washers and insulation tube over the rod, then removing eg the fibre washer from one end so that the rod electrically connects to bell-end and core can be ok, as there is still no current loop through the rod, as the other end of the rod is still insulated.
That is normal. I never had a short through a bobbin unless it was struck by lightning. A long time ago there was discussions between OEM repair techs, engineers, electricians and the UL regulatory on how we could apply earth ground bonding in appliances (not just audio equipment) for GCFI protection.
You guys have something simular but yours I think ground at the chassis then the transformer is either bonded (and tested) to the chassis or a lead is brought over to the chassis grounding point. But if its not certified that the bond testing is done, then the wire has to be connected.
Laminates are purposely insulated with a coating so they don't short together and cause Eddie currents and core loss.