SWA from transformer to DB

[johnboy6083]

im a numpty, if course you cant induct into a non ferrous metal. hence te AWA. I wasnt aware that you can get SWA singles for the reason you mentioned.

 

[Knobhead]

im a numpty, if course you cant induct into a non ferrous metal. hence te AWA. I wasnt aware that you can get SWA singles for the reason you mentioned.

Neither was I, all the transformers I’ve worked on had either double insulated or lead sheathed tails. Aluminium never crossed my mind!


The thread started with SWA armoured singles!

 

[davelerave]

Neither was I, all the transformers I’ve worked on had either double insulated or lead sheathed tails. Aluminium never crossed my mind!


The thread started with SWA armoured singles!

are there any issues with earthing both ends of swa in general

when does this become a consideration?

 

[benji]

no problems if you use non-ferous gland plates

yours benji

 

[Alpha Spark]

Another reason could be, that with the armour's connected, the ZE will be tiny. Less that 0.01ohm. This will lead to a massive PFC.

 

[davelerave]

Sorry this is a bit late.

Armoured transformer tails are unusual, normally double insulated un-armoured. The reason for glanding just one end is to stop the armour wires becoming a giant 1/1 CT. At full load your 500KVA transformer would have 666A flowing in the armours.

I once had a situation where 1000KVA transformer was installed and the contractor decided that the brass gland nuts we’d provided were to nice to use so substituted steel, it was in a bolted terminal box so who would know. Things were OK for a while but as the load on the transformer grew so did the heat. I’m just glad I wasn’t around when the insulation finally melted in the transformer terminal box

The contracting company wasn’t around for long after that!

still don't quite get this- are eddys currents an issue on swa's generally

SP and 3P if 'banjoed and flylead' both ends

ie: cpc and armour paralleled


or is it just singles ?
thanks for any info

 

[Knobhead]

With aluminium armouring or lead sheathing one end only will be earthed to stop circulating currents. I went back through my old apprentice training books to find out why we didn’t use aluminium armouring, all the plants produced or processed lime. Aluminium and lime isn’t a good mix, the lime rots the aluminium away, and for the same reason aluminium ladders weren’t allowed. Lead has to be plumbed to terminate it so the cores can be sealed with compound. Each plumbing cone at one end would be insulated from the terminal box. From what I’ve found out aluminium can be glanded at each end but one end like the lead must be insulated. On all the systems using lead the transformer end would be earthed while the switchgear end would be insulated.
Some of the transformers were installed with aluminium conductors but the terminations had to be protected from the lime with a horrible spray on yellow gunk that for the life of me I can’t remember what it was called.
My comment about eddy currents referred to an episode where a contractor used steel locknuts on double insulated singles instead of the brass he was supplied with. The gland plate was steel but with slots and the glands brass to stop the eddy currents, he f*^ked it up by pocketing the brass locknuts.