obscure regs

[supasparxs]

I'm writing an EICR in a department store in London

one of the section boards has a sub-main made up with 4 x single core 95mm MICC cables.
I have snagged that the gland plate is steel and there are no slots in place to counter the eddy currents.
(the loading is only 15 amps per phase when testing at about midnight)

But inside the section board the MICC's connect into a large set Din rail terminals to 35mm singles into the 100 amp MCCB.

I seem to remember that there is a reg basically stating where ever a conductor changes size there needs to be additional overcurrent protection

any ideas anyone?

 

[Bobster]

Eddie currents - problem

change of size - not necessarily a problem, certain factors need to be taken into account.

 

[davesparks]

The reg allows protection to be placed after the point in reduction of CSA if the cable is protected from mechanical damage and less than 3metres long etc etc. Based on the information you have given there doesn't appear to be a problem. It is likely that this has been done due to 95mm solid cores not making a good connection to the mccb terminals.
Also the internal wiring of a panel is most likely subject to different regulations.

With the eddy current problem, are you sure the glands have to been insulated from each other at one end or had slots cut at one end?

 

[Leesparkykent]

You want to be looking around Reg 434.2.1 or reg 434.2.2 off the top of my head.

 

[Richard Burns]

Where the entire run of the circuit is suitable for the protective device then there is no need to add additional protection at any reduction in csa since it is already protected at origin.
If there is a reduction is csa such that the cable is no longer protected by the protective device then another protective device, that does protect the reduced csa conductor, should be placed in circuit.

 

[Deleted member 9648]

Eddy currents are not normally a problem in cables carrying less than 200a....as this is a 100a supply it shouldn't be an issue.

 

[DPG]

Eddy currents are not normally a problem in cables carrying less than 200a....as this is a 100a supply it shouldn't be an issue.

Is this definitely true? I would have thought a 100A circuit could have problems with eddy currents if plate not slotted. Daz

 

[Darkwood]

Eddy currents are not normally a problem in cables carrying less than 200a....as this is a 100a supply it shouldn't be an issue.

This is the general concensis although you should still takes measures to prevent it, i the OP case the set-up will be affected by Sheath eddies and these will exaggerate the effect and can cause issue at lower ampage .... I've come across a switch bank with 3 phase supply entering through different metal conduits (2/1split) which commoned on the M/C switch and the steel trunking 1m above... with <20amps in load per phase the conduits were too hot to touch and starting to exceed the limits of the 70'c singles insulation... all you require is the effect to start and heat disappation to be slow and you get a runaway effect even at low ampage.

The 200amp rule is where is becames an issue in most circumstances regardless and just explains why you may not see its effects at lower levels but we mustn't get complacent over the rarer occasions that it is an issue <200amps because under the right conditions its just as dangerous.

 

[netblindpaul]

621.5?