Type C or D MCB breakers?..

[tony sayer]

We've got a remote location that has a few hefty power supply units therein just simple transformer rectifier sets that supply a DC buss bar which a lot of other equipment runs off with individual regulators on etc. Problem is good ole EDF will keep switching the line and that sometimes causes the breaker feeding this circuit a 32 amp one to trip all at awkward times ;!..

Like 5 am this morn!..

Q. I believe that a Type C breaker gives some measure of anti surge for this heavy inrush current application but there is also a type D is that any better or a different thing altogether?..

TIA...

[Bill]

In message , tony sayer writes

Tony, Get the Meccano out and build a mechanical device that will rest the breaker say 3 times and if it continues to trip then stop trying.

I do love these early morning call outs for power loss. Had one to Wimbledon a couple of years back. Someone had turned a multiblock off that was powering a local base. Not amused......

[Andrew Gabriel]

Basically, Type B, C, D all have the same thermal trip (overload) protection, but have increasingly higher magnetic trip (fault) protection. Type D is not normally required, and brings with it several other factors which you need to bear in mind, such as discrimination with upsteam protection, requirements on earth fault loop protection, etc. I haven't checked, but you might find it's impossible to use a D32 MCB with a standard residential main fuse, without the main fuse blowing first in some circumstances.

[tony sayer]

In article , Andrew Gabriel scribeth thus

Type C it is then ..

Thanks for that:)

[NT]

Type D would get you less tendency to trip if its usable. Wire fuses would also reduce the trip proneness, but the obvious downside might be unworkable.

You could also look at the power supplies and see what can be done with those to reduce the inrush. One simple option would be to use a relay that has them start up on a half output voltage tap, and after a second or so switches to full output voltage. Another option is a series inductor on the mains side with a relay that shorts it out after a second or so. Relays are easily delayed using a deiode, R, C on the coil side.

NT

[ARWadsworth]

Is this a ring with 2.5 T&E cable? If so the OSG gives the maximum length for a 32A type C MCB as "Not permitted" on a TN-S system and maximum lengths of 82m for an RCD protected circuit and 63m for a non RCD circuit on a TN-C-S supply.

Cheers

Adam

[Andrew Gabriel]

Another option might be to change to a BS1361 cartridge fuse carrier. They seem less trigger sensitive than MCBs, but are still fast acting when they need to be.

Obviously, when you change the circuit protection, you need to make sure it's still suitable for the circuit, considering the earth fault loop impedance (excluding RCD-protected sections), and the required disconnect times at socket outlets, etc.

[John Rumm]

The three types have the same response to sustained overload, but different responses to clearing faults (i.e. short circuits, or hard faults to earth). This "instantaneous" trip mechanism kicks in at 5x rated current for a type B, 10x for a C, and 20x for a D.

See the curves here for more information:

higher letter takes progressively more design effort to get a system that will work as intended. Type Ds can can be difficult to use in many cases. Cs will depend on the length of the circuits, and the type of cabling, and whether RCD protection is in place (or for that matter desirable). Note that in circumstances where a RCD is required to meet the earth fault protection requirements, this does not have to be a

30mA trip device since its purpose here is for equipment, wiring and fire protection, not shock protection.

[Dave Osborne]

You need a type K circuit breaker or you need to change to a fuse.

[dennis]

Cartridge fuses are one solution. SystemX uses fuses so they don't trip.

[tony sayer]

In article , ARWadsworth scribeth thus

Its all of 2 metres from the dis board and is RCD protected, another source of intermitting tripping usually during storms;!..

[tony sayer]

Yes could do that but it think if a differing breaker does the trick less bother all around...

[tony sayer]

In article , Andrew Gabriel scribeth thus

As per other post thats what we used to have with no problems;!..

[tony sayer]

Well I do have a shock protection requirement as this is rather remote location and lone working goes on there, and we had a very close shave whilst working alone least year, not electrical, so RCD it is and if there are a few odd trips then something we can live with!..

In practice there're very rare and usually due to close thunderstorm activity..

[ARWadsworth]

Is there any easy way to split the loads into two circuits and use two MCBs?

Cheers

Adam

[tony sayer]

In article , ARWadsworth scribeth thus

Bit awkward to do, but I'm minded to change the breaker and then try that to see if its OK and if so leave it at that..

Cheers..

[js.b1]

Do the PSU specs have inrush current data?

1 - Put each PSU on its own breaker. Thereby reducing the combined inrush per breaker, ie, from 5 PSU chomping 80A (400A) to 1 PSU chomping 80A. DIN rail BS1361 HRC fuse can be a good one, but it depends on what is upstream. 2 - Use a power sequencer Commercial or DIN rail jobbie made up of process eng stuff 3 - If EDF is "warbling" the line on reconnection you could use an auto-reconnector These basically wait for "power good for 5 sec" before repowering stuff up, can not recall the technical name.

There are auto-resetting devices re lightning for just this situation.

[NT]

Go back to it then, problem solved. Spare fuses, or with rewirables, which I far prefer, a spare carrier and fusewire card, will avoid delays. Both fuse types are stll legal.

NT

[John Rumm]

If the circuits have RCD protection for shock protection, then that also works for protection from high earth loop impedance anyway. ;-)

[tony sayer]

No..

We can do ..

Bit overkill for this site!..

I suspect its a recloser doing its bit when the trees are walloping the lines as they are won't to do sometimes!..