400 amp bs88

[ganzo]

Hi

We have a LV section board supplied with 630mm singles. The ammeter on the board is reading 530 amps per phase. We checked upstream and it is supplied from 3x400amp bs88 fuses. Can anyone explain why the fuses can take this load without blowing. If so where can I get some documentation to back this up.

Thanks

 

[Darkwood]

Did you take the fuses out and confirm the rating or just read the label on the switchgear?

 

[bigdavs83]

530 amps per phase?! That's impressive load balancing! As darkwood says are the fuses definitely 400a?

 

[ganzo]

Took the fuses out mate 400 amp all the way?

 

[ganzo]

Load fluctuating between phases but averaging around 530

 

[Plonker 3]

May be time to get a calibrated clamp meter out?

 

[Darkwood]

You need the time/current curve for a 400amp bs88-2 at 530amps it will be unlikely to blow the fuses straight away but after a good duration ... I doubt this is a average demand you measured or they would have been taken out by now.


I will assume you have a calibrated clamp meter.

Check the max Kwh demand on the meter by cycling the button most let you do this...

How exactly are you measuring this value?

 

[ganzo]

What is the max that a 400amp fuse could cope with?

 

[Darkwood]

What is the max that a 400amp fuse could cope with?

Your not reading my replies as this is a overload their isn't a max you can apply you look at the current/time curve for the fuse and it will give you how long in seconds the fuse will hold for if that current is maintained.

If you are correct and this current was maintained the fuses will operate - what is the average value on your meter and again with what and how are you measuring it, and are you doing it correctly. I ask because like most you fail to fill your profile in so we have to ask you in simple terms as we can't guess your experience and qualifications.

 

[ganzo]

The load is fluctuating as its a waste transfer site with lots of motors. There is a lcd display on the main incoming section where you can select kw amps or volts. I say 530 amps average per phase as the display is changing constantly.

 

[Plonker 3]

Fluctuating between what?

 

[ganzo]

490-550 amps

 

[Darkwood]

Your seeing load spiking as the big motors this is especially common with shredding machines etc, the overcurrent last for a few seconds only before dropping back down.

You may want to review the sites KVA demand and your KVA allowance and see if you need to take measures... as you have ask this question to start with and seeing your confused with what your seeing and how to relate it to a time/curve chart then you may need to get an experienced person in to see if measures need to be taken before you end up with a power outage.

Have you any electrical background or you asking from a curious point of view with no training in this field?

If the DNO meter has buttons for cycling reading what does the max demand say in KVA or KwH?

 

[Chr!s]

The fusing factor I2 for a Typical BS88 400 is 1.6 In for four hours. Stick a power logger on the system and analyse the data if you are concerned.

Chris

 

[Knobhead]

You have got to log the usage over a shift at least.

I’m surprised the DNO has allowed consistent overload for any length of time. We were penalised if we overstepped the mark.

 

[ganzo]

Thanks for the advice guys. Not in work at the moment but will have a another look tomorrow and hopefully get more details. That's if the lights are on.