Eddy Currents

[snowhead]

I'm beginning to think that people are not treating this matter with the solemnity and respect that it deserves....

:grinningelf::grinningelf::grinningelf::grinningelf::grinningelf::grinningelf::grinningelf::grinningelf::grinningelf:

 

[Knobhead]

The layout I always used for transformes and switch gear when using singles.

E54 would go for a paxoline gland plate, under the regulations (M&Q) I worked to it had to be steel.

 

[Crosswire]

The layout I always used for transformes and switch gear when using singles.

E54 would go for a paxoline gland plate, under the regulations (M&Q) I worked to it had to be steel.

Forgive my ignorance, but why seven holes ( assuming a three phase supply)?

 

[telectrix]

in and out?

 

[Guest111]

Forgive my ignorance, but why seven holes ( assuming a three phase supply)?

3 lives in,3 out and 1 earth?

 

[Knobhead]

Forgive my ignorance, but why seven holes ( assuming a three phase supply)?

For hight current it is better to use two smaller conductors per phase (look up skin effect). The neutral normally only needs one conductor.

Modern practice due to harmonics is to use two.

Where high unbalanced harmonic loads are expected. The transformer will be rated type "K" and three neutral conductors provided.

 

[Crosswire]

For hight current it is better to use two smaller conductors per phase (look up skin effect). The neutral normally only needs one conductor.

Modern practice due to harmonics is to use two.

Where high unbalanced harmonic loads are expected. The transformer will be rated type "K" and three neutral conductors provided.

Ah I see.

So where does this leave 521.5.2

" Single-core cables armoured with steel wire or steel tape shall not be used for an a.c. circuit"

Is there something I am not understanding about this Reg? I have a site with massive single core cables all run in swa. Does this Reg not apply to sub mains?

 

[cossie400]

Ah I see.

So where does this leave 521.5.2

" Single-core cables armoured with steel wire or steel tape shall not be used for an a.c. circuit"

Is there something I am not understanding about this Reg? I have a site with massive single core cables all run in swa. Does this Reg not apply to sub mains?

They may well, and most probably will be AWA's. (Aluminium wired Armoured)

 

[Crosswire]

They may well, and most probably will be AWA's. (Aluminium wired Armoured)

Ah that makes sense. Good thinking Batman!

Do they then still need to be slotted when terminated onto a metal trunking, as described above?

 

[cossie400]

Ah that makes sense. Good thinking Batman!

Do they then still need to be slotted when terminated onto a metal trunking, as described above?

Hell yeah!!!!

The steel trunking is the issue, as it's ferrous and contains iron, it will have to be slotted.
if the trunking or a gland plate was made from aluminium or brass for example it would not need to be slotted as it is non-ferrous.

 

[Crosswire]

Hell yeah!!!!

The steel trunking is the issue, as it's ferrous and contains iron, it will have to be slotted.
if the trunking or a gland plate was made from aluminium or brass for example it would not need to be slotted as it is non-ferrous.

OK cool. I will check the glands tomorrow. The Big Boss is coming to site and I will pick his brains on the subject.. Thanks for the help dude!

 

[Knobhead]

They may well, and most probably will be AWA's. (Aluminium wired Armoured)

AWA is a strange one. Only one end of the armouring should be earthed otherwise circulating currents will pass between each end of the cable.
Not eddy currents but circulating currents.

I’ve got a Reyrolle installation manual for 11KV gear from the 30’s. It shows using single core PILC, even with lead the sheath can only be earthed at one end.
If the singles are between a transformer and a switchboard it is normal to earth the sheath at the transformer end only.
There are reasons for this due to the use of restricted earth leakage relays to protect the transformer.

Eddy and Circulating currents are two separate but inter-related subjects.

 

[scammell man]

521.5.2? try 521.5.1

 

[Lucien Nunes]

For high current it is better to use two smaller conductors per phase (look up skin effect). The neutral normally only needs one conductor.

If the singles are between a transformer and a switchboard it is normal to earth the sheath at the transformer end only.

Paxolin at t'other end, in the panelboard in our workshop.