Toroid bolt clearance

[cpemma]

Important: under no circumstances should both ends of the fixing bolt be allowed to come simultaneously into contact with the metal chassis so that an electrical path is formed through the bolt in the centre of the transformer via the external chassis. this would result in a direct short and cause considerable damage. A clearance of 4mm must be allowed over the mounting hardware.

From the supplier's blurb here.

I understand the shorted single-turn business, but the last sentence has me confused. I'm wanting to put a toroid in a die-cast aluminium box, top clearance is about 1mm. My plan was to glue a couple of thicknesses of a fine-weave fibre-glass mat I found across the toroid's steel washer and bolt-head to act as insulation against any accidental pressure on the box lid, but is there some danger I've not considered?

[poobah]

A thin sheet (15-20 mil) of pvc or polypro plastic would be better... fiberglass is porous... sparks go right through. There are plastics made just for this. The 4mm refers to free air clearance most likely.

check out ITW Formex GK-17

[Eva]

The 4mm clearance requirement is because traditional cases are made of thin steel sheet at best, and the sheet bents easily, so it may make contact with the screw unexpectedly.

You may consider cutting the excess length of the screw and placing a sheet of some heavy duty insulating material between the toroid and the top cover.

[AndrewT]

Hi,
I agree that the 4mm clearance takes account of case flex and air gap.

I always insulate the steel plate and bolt with two layers of sticky insulating tape applied at right angles with a 55% overlap between each tape. This guarantees 4layers and is very robust against accidental damage.
1mm repeatedly flexing & touching would then not bother me.

[cpemma]

Thanks for the responses, checking various manufacturers I can't find a repeat of the 4mm clearance warning, but Nuvotem advises on toroid dimensions to allow an extra 4mm on the height dimensions quoted for mounting hardware. This figures, the toroid I have is specified as 46mm high but bolted down it's more like 51mm, and that's with bolt head up.

[PROSTAKA]

Hi
it's my toroidal transformers

[AndrewT]

Hi Prostaka,
that labelling on the fourth transformer is incorrect.

220V,0,100V

The two wires going into the 100V labelled connection need to be separated and rewired to enable 110Vac duty.

Remove the 100V label just in case some poor soul mis-interprets the information.

[davidlzimmer]

How bout a teflon bolt?

[PROSTAKA]

Hi
I am sorry AndrewT, but on the 4th label I've made a transformer for special devices that work on 100 V

[BrianDonegan]

I've been using funriture connector bolts and cap nuts for my trafo mounting. Keeps the protrusion low on the bottom of the case, and the top of the nut stays inside and below the height of the top trafo washer.



812-543 and 812-620 in the pic. You can get them from woodworking suppliers, and I'm sure, lots of other places.