MCCB vs HRC overcurrent protection

[Knobhead]

Come-on Tony, ....So what's this plant panel actually a part of?? Spill the beans...lol!!!

The arse end of a kiln contactor panel. The contactors were mounted on the “posh” side, all polished slate and brass. It was a joy to work on.

 

[baldsparkies]

HRC fuses are used by the DNO because fuses present the cheapest method of providing PSCC protection to an installation...

From what you describe, as in the ''Blips'', This can easily be protected against by provision of Surge Protection.

I don't know of any manufacturer of MCCBs that have a setting range on a 400A breaker of 160A to 400A!! I think that your 400A is a frame size, and that the actual size of this breaker is in the region of around 280A to 300A, depending on manufacturer.

Are you saying that this breaker (MCCB) is single phase, or just that the final loads are single phase?? If it is the latter, the UPS isolation transformer along with many other components in the UPS will be 3 phase and will not like at all, a situation where it's supply is single phasing!!!

If you can give a little more information, after you have been back and assessed the situation on this installation it would be helpful, and a pic or two even more so....

Just an update, It is indeed a 160 to 400 amp MCCB Merlin Gerin NS 400H.
Phoned Schneider Technical today, and they were very helpfull, with all the info I needed to have a little play with the blue dial thingy's.
I also made sure the mother wouldn't tripp under load, consequences would not have been good
6 calibration dials in total marked Io Ir tr Isd Ii and tsd. So plenty to play with.
Anyway, all settings were set to minimum which is the manufacturers default settings, not maxed out as I was told (Just goes to show).
Only one to watch for is the let through current on the pfc, but other than that all good after recalibrating. (He's lying, he chucked it away and used the 6" nails )
So all done and another happy customer, Thanks for all the replies and advice lads, much appreciated.

 

[johnboy6083]

hi baldsparkies. is there any chance you could elaborate on the advice you received, so that i could learn a little too please?
what do all of the letters mean? ect ect.

thanks mate,

john

 

[baldsparkies]

hi baldsparkies. is there any chance you could elaborate on the advice you received, so that i could learn a little too please?
what do all of the letters mean? ect ect.

thanks mate,

john

Here goes Johnboy, I will try to sound intelligent

Io and Ir set the overcurrent tripp threshold, with In being the nominal rating of the MCCB
So if In is set at 300A Io at 0.7 and Ir at 0.8. you multiply 300x0.7x0.8 to give you 168 amps.
Isd sets the let through current for the pfc under short circuit conditions.
And tr and tsd set the lag times respectively.
All in all very much like the 3 dial set up units with the luxury of adjustable time lag, (Still doesn't beat the 6" nails though)

 

[Knobhead]

Still doesn't beat the 6" nails though

6” nails? Go for the no blow specials!

I had a 4000A breaker fail, the isolating mechanism jammed when I tried to get it back in to service. So in desperation I used the old short it out method. 2am is not the time to be looking for old copper bus-bars but I managed to find 10’ of 2½ X ¼” bar and bridged the ACB out. I had to limit the power to just 3000A as I couldn’t find enough copper to allow full power through.

 

[baldsparkies]

Nice to see a hands on thinking sparkie out there Tony,
Ever thought about Astronomy ?? They still haven't decided on the big bang theory, lol.

By the way, one thing I did have verified was that under load adjustment with these units is possible. You are safe dialling up ie increasing but NOT down !!
If your load is reliant on a constant supply (Mine was) then downward adjustment could cause the device to tripp, if you dial below the tripp threshold.
Might be usefull to some of you guys one day if found in the bricking it situation.