Lift power supply disconnection time

What is the rating (amperes) of the lift supply circuit ?


ie - does if fall into the description in 411.3.2.2 and thus Table 41.1


Regards


OMS

It is a 16A MCCB

OK - that looks like 411.3.2.2 (ii) then


So 0.4 seconds on TN and 0.2 seconds if TT


Regards


OMS

Thanks OMS

I am just wondering why 0.4s though.

I mean, I have in front of me the schematics of the lift control panel and the lift will fuse individually each of the downstream supplies. Doesn't seem different than a typical DB.

Could you elaborate on this?

Well, I guess you could interpret it every way you want - for me, for simple compliance, if you assume the lift is a "black box" covered by it's own standards, then you are putting a final circuit in to supply that box.


As the rating is less than 32A, then BS 7671 would suggest that you use 0.4 seconds as the TN disconnection time


Given that you have a 16A MCCB proposed, unless you have a particularly ropey supply source, then achieving 0.4 seconds shouldn't be a drama


I've no idea where you intend supplying the shaft lighting and pit and car top control sockets (or is it part of the lift specialist contract) but if you look at (i) of the regulation, you might conclude that you need 0.4 seconds anyway (although you could expect that the lift supplier does have protection on that socket outlet that would comply in all respects with BS 7671 and the major parts of EN 81)



Your circus, your monkeys - so up to you as the designer which way you go. I'd err towards simple compliance personally


regards


OMS

Or if all the loads downstream are protected, and really you are worried about it tripping when it should not, then lay in cable for a higher rated breaker. I'm assuming it is SWA or in conduit, so no RCD needed.

Yes.

It is 4c 4mm2 XLPE/SWA with 16A protection as per the lift manufacturer requirements.

The lift manufacturer was asking for 2.5mm2 cable but it is 100m ride hence my problems.

So it is 4mm2 now plus a separate earth.

Cheers

What does voltage drop on lift "start" look like, with a 100m run ?


Regards


OMS

This is a good question. 

I do not have the exact answer for the "starting" mode, however from the manufacturer data sheet I know that the nominal line current is 14A and RMS acceleration line current is 17A.

The lift has a variable speed drive.

So my preliminary assumption is that the voltage drop will not be an issue.

Regards

Might be worth you checking that  - 4.0mm2 is a fairly slender cable for a 100m run coupled with a start current already exceeding the MCCB nominal setting in terms of voltage drop


If it really is acceleration current, it may be sustained for a reasonable time step - which is certainly going to start warming up the thermal part of the MCCB


Regards


OMS