sizing up mcb and a contactor

[damunk]

I have a servo drive that is rated 10AMP. It then has a second rating refered to as it's Peak current : 30AMP

1) Do you size a MCB using the Peak current rating or the standard rating?
2) Again when choosing a contactor would you go for one closest to it's peak current rating or standard current rating?

I am also thinking of chucking in a efi noise reduction line filter if someone could guide me a suitable one . Thanks,

 

[James]

have a look in the instructions for the drive.

it will recommend both incoming protection and emc avoidance measures required.

 

[damunk]

it's a chinese drive and all it says it to make sure a circuit breaker is used.
the only relevant info is the current it draws and the peak current of 30A

 

[James]

It is unlikely to have internal filtering for emc!

check the voltage rating, many chinese drives use 3phase 200v phase to phase
as a rough estimate, I would expect a 10A drive (output 3phase) if fed from a single phase supply to require a 40A supply.
if it is 3 phase input then 16A will suffice.

 

[pc1966]

I would also be sceptical of it meeting any EMC standards so an additional filter would be a very good idea. Be aware that, and VFD in general, can have quite high earth leakage so you might need to allow for that if RCD protection is in use.

RCD protection is not often needed for fixed supplied equipment, but in some locations or if fed via a plug and socket you might well need that.

For MCB you can usually buy them with different magnetic trip points, so:

• B-curve has 3-5 * In
• C-curve has 5-10 * In
• D-curve has 10-20 * In

In the absence of specific manufacturer's advice, if the running current is 10A then typically you would be using the next MCB size up = 16A. Then a 16A B-curve has the "instant" trip at 3*16A minimum = 48A or more so might be adequate if that 30A really is the peak current, however, for more traditional motor starting you might be looking at C-curve or even D-curve.

But don't assume the D-curve is always usable. For fault protection you need to make sure that it will trip in under 0.4s so the L-E loop impedance has to be sufficiently low for the chosen MCB so under minimum supply and hot cables you can meet the upper magnetic trip point to reach such a fast disconnect.

For example, a 16A D-curve MCB needs 20*16 = 320A to guarantee such a trip, allowing 0.95 * 230V for minimum supply and 80% for cables running hot then your maximum Zs is:

Zs = 0.8 * 0.95 * 230 / 320 = 0.54 ohms

That is not always possible if your supply Ze is in the higher range! (E.g. for TN-S that can be as high as 0.8 ohms and still "normal")

 

[damunk]

just confirm it is not 3 phase. it is a standard UK 240V 3 pin plug.

 

[damunk]

It is unlikely to have internal filtering for emc!

check the voltage rating, many chinese drives use 3phase 200v phase to phase
as a rough estimate, I would expect a 10A drive (output 3phase) if fed from a single phase supply to require a 40A supply.
if it is 3 phase input then 16A will suffice.

 

[damunk]

It is unlikely to have internal filtering for emc!

check the voltage rating, many chinese drives use 3phase 200v phase to phase
as a rough estimate, I would expect a 10A drive (output 3phase) if fed from a single phase supply to require a 40A supply.
if it is 3 phase input then 16A will suffice.

Thanks guys for the prompt replies. James it is single phase 240V . Would that mean I have to go with a higher mcb or shall I start off with lower ones as I can always go with higher ones later. I’d just like to get something going before I get an electrician in to check it out all because electricians as you know are even busier than ever and I want to be able to show the electrician that I have some sort of clue what’s going on lol

 

[James]

just confirm it is not 3 phase. it is a standard UK 240V 3 pin plug.

In that case it is fused at 13A in the plug.

 

[damunk]

In that case it is fused at 13A in the plug.

So that’s all that is needed?
Because I was going to install 6 of these servo drives in an electrical
Cabinet.

So you advise just to keep it simple and leave it with fuses.

I was dreaming of a very pretty electrical layout within a electrical enclosure so you advise that it is best just to put some 6 way gang sockets and just plug em
In simple… hmmmm

 

[pc1966]

So that’s all that is needed?
Because I was going to install 6 of these servo drives in an electrical
Cabinet.

So you advise just to keep it simple and leave it with fuses.

I was dreaming of a very pretty electrical layout within a electrical enclosure so you advise that it is best just to put some 6 way gang sockets and just plug em
In simple… hmmmm

If they are plug & socket they have to be RCD protected and with that many drives you are likely to have issues of accumulated leackage causing false trips if it is a single supply.

Also if you have 6 drives each of 10A and any real possibility of them simultaneously running at rating then you need a 60A supply in total, that is going to require 2 * 32A feeds for the lot, even if they are each on 13A fuses at the end.

To avoid the plug & socket and thus RCD requirement you could hard-wire them in to FCUs instead, so say two 32A radial so 4mm cable (if clipped direct and not in hot zone or thermal insulation) each supplying 3 drives via 3 FCUs would be an option.

If they have to be removable thus plug & socket you would need to investigate the leakage, as you might have to put in 3 * 25A RCBO feeds or similar with each doing 2 * 13A socket, etc.

 

[James]

1 drive, as you said comes fitted with a plug, easy.

6 drives in an enclosure needs a proper design process and is out of the realms of a little diy advice.

 

[Rockingit]

Hard wire individual circuits back to DIN fuse carriers?

 

[pc1966]

Hard wire individual circuits back to DIN fuse carriers?

Yes, that is an option to have a DIN box of them and then a 63A feed from the main panel. Finding a suitable bus-bar might be harder if so many on single big supply.

Might be just as easy to have a local CU of 6 * 16A MCBs!

 

[damunk]

im stucknow,

so 6 mcb's with magnetic contactoras suggested in manual drawing for 3 phase althought imusing singephase 240v (theres no drawing for that)

or 6 din fuse rail way.

and using 6 bus bars (3+3); 2 for live 2 for neutral and 2 for earth. and using two seperate 40A feeds from main power box.

sounds good yeah?