MCCB vs HRC overcurrent protection

[Knobhead]

Is it possible to add an alarm
To call maintenance if the mccb tripped

It’s a bit late by then, the problem has to be stopped before it starts.

Quote the plant manager “did you know the main breaker’s tripped again?” Me “yes the fu**ing kettles stopped boiling and it’s bl**dy dark in here!”

Discrimination and trip settings are a nightmare when you get to 400A+ breakers, as Baldsparkies obviously knows. Both time and current are adjustable so it’s easy to alter one setting on the local breaker and move the problem one step up the ladder.

 

[baldsparkies]

Don't worry Tony, I shall be taking some 6" nails up with me.

 

[johnboy6083]

Aint that the truth Tony, Often with the bigger companies, they have various contractors adding here and adding there with no one keeping check on who's doing what, where and why. I remember on one site Red phase had 80 amps Yellow 260 and Blue 140. But it happens all the time, at least on this one the phases are pretty well balanced so no issues there. Thanks for the responses to all.

Very true mate. the sites im working on, nobody has a clue whats in them and what isnt. half of them are not even fully functional, and trying to find out anything ie teste results ect, is a nightmare.

at the moment, they have employed another frim to carry out PIR's, but they are also testing our firms half finished installs, failing them, as they are not complete, and ive still got to test them when they are fininshed. i reckon that the firm will bill for remedials, and when thhey turn up to carry out the work, wuill find it all kosher, cos we would of finished, and earn for nout.

its a shame that electrical safety isnt a priority.

 

[Knobhead]

its a shame that electrical safety isnt a priority.

The eternal cry of the maintenance / industrial electrician.

 

[johnboy6083]

ill try and get some photos of some of the gear i see. its ancient, but sill works. in one place there are 2 massive generators, one english electric, and one blackstone. they have DC generators at the end, on the same shaft, which i guess are being used as exciters. a small petrol engine acts as the starter. its a shame, but both of these beasts are no longer operational. the panel for the blackstone genny must be 50's, and still in good nick. ive opened some of the cubicles, just tp noes at the wiring, and its the neatest ive ever seen.

 

[baldsparkies]

Would be interesting to see Johnboy. The fact there still operational is testament to the quality of build with the old stuff,
I mean look at me. Born in 1953 and still going strong, keep tripping over the zimmer frame though.

 

[johnboy6083]

i was born in 87, and keep breaking down! lol

 

[Knobhead]

I was heart broken to take this out and replace it with modern crap. Just a pitty I didn’t get a picture of the front, polished black slate

View attachment 5718

We even had a mercury arc rectifier.

Meet Rodney

View attachment 5719

Used to scare the living daylights out of me at first, but then I got quite fond of it. To watch it working was like watching a living thing.

 

[Engineer54]

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

 

[johnboy6083]

that looks like a work of art. im actually an industrial pervert, but half the tiome i dont know what im looking at!

 

[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.