Bizarre supply issue

[Dizzy_Maskell]

Chaps,

Carrying out an EICR on a pool/spa this morning.

Local switch panel in the plant room old bs88 switchgear 1600 amp.

Issue was this DB2 was full of RCBOs about 12 way TP&N all IR clear,

When re energised all RCBO fine and stayed in at the same time I was testing this my mate was testing DB4 in another room entirely.

When he turned his board back on every RCBO in DB2 tripped instantly.

When I tried to test the RCBOs in DB2 as soon as I touched the neutral probe on they all tripped.

Additionally as I tested DB1 the blue phase fluctuated sometimes it was there other times it was not but in the end after numerous voltage tests it seemed to stay.

All neutrals in DBs where tight and all supply cables IR ok.

Each board fed from a separate bs88 fused switch on the switch panel and completely separate.

If any of the other fuse boards where turned off and on every RCBO in DB2 tripped instantly.

I'm guessing this is done kind of neutral to earth fault with the supply side,

Has anyone else ever encountered this.

 

[Richard Burns]

Blue phase (you mean you haven't updated to grey!:stuart fluctuating, if you mean that the voltage to Earth / Neutral was not present at times, this sounds like a loose phase connection that would need addressing quickly.
Are the RCBOs single or three phase?
All I can think of is that the volt drop on switching on another board causes the loose phase to disconnect and give a surge through the RCBOs, but this should not affect RCBOs on another phase.

 

[jackhammerJIM]

Each board fed from a separate bs88 fused switch on the switch panel and completely separate.

If any of the other fuse boards where turned off and on every RCBO in DB2 tripped instantly.

are the mainswitches for DBs 4 POLE ?

could be a borrowed neutral .

 

[Darkwood]

Why are you (de)+ energising dist boards with all outgoings switched on?? Your asking for trouble....

What loads have you attached to the boards I.E. inductive lighting , motors etc if the installation is large with multiple inductive lighting loads in particular you may have switch on a massive inrush current over the phase by using the main switch to flip the boards on and off on load without dropping out the individual circuits.... the way you word it this is the impression that comes across and can create very large mains transients.

Can you elaborate more on your testing .. was the system heaily loaded when the phase voltage was fluctuating, is their any other symptoms with the installation, if blue phase is fluctuation wildly this would be evident is lighting flckering etc...

Ensure your are not testing to a terminal that has been lacquered for anti-corrosion which can fluctuate any probe placed on them... if you can access the cable copper try the test again..

 

[Knobhead]

What make is the switchgear? Both main board and sub boards.
Where are you measuring the voltage L→N or L→E and where in the system?
How well balanced is the overall loading?

 

[Dizzy_Maskell]

In reply to above the board he turned on was not under load all circuits where off and it was turning the board on that caused all RCBO to trip.

The main switches are 3 pole yes I suppose borrowed neural but seems bizarre on a main supply when all supply cables go out of separate switches from the bs88 switch gear

 

[Dizzy_Maskell]

What make is the switchgear? Both main board and sub boards.
Where are you measuring the voltage L→N or L→E and where in the system?
How well balanced is the overall loading?

The loading on the DBs appears well balanced all DB are hager supplied from a old mem switch panel I reckon years before I was born.

I think the installation was redone some years ago and the old switch gear left in.

 

[Dizzy_Maskell]

I was measuring the voltage on the fluctuating blue phase at the incoming side of the DB with the main switch turned off.

 

[Darkwood]

Just to clarify you say the boards were switched on - off load (all outgoing circuits switched off), so you were only energising the the DB's internal busbar?

When we say turning the board on IE DB4 we are talking at the DB4 main switch or do you mean upstream at the supply for DB4?

 

[telectrix]

is this local, dizzy? IIRC, you're based near to me.

 

[Dizzy_Maskell]

Yes he only turned on the busbar of the DB.

 

[Dizzy_Maskell]

is this local, dizzy? IIRC, you're based near to me.

Yes mate how's you?

 

[telectrix]

not 3 bad. work's a bit quiet, but a couple of biggish ones coming up.

 

[Dizzy_Maskell]

So anyone any further comments on this issue,
We informed site and left them to look into as we had finished (they have their own electricians btw)

 

[snowhead]

I'd say a bad connection on a lug (poor crimp/loose bolt) or clamped connection, most likely Blue, possibly N as well.

I'd be looking at;

Checking the voltage across all phases and phases to Neutral as far upstream as possible to see if it was stable coming in.

Then put a meter across all lugged or clamped connections to see itf there is any volt drop or variation

 

[Dizzy_Maskell]

Sound good, voltages 230 L to N on all phases

 

[Darkwood]

If you switched DB 4 on at DB4's main switch and all outgoing were switched off then all you are doing is extending DB4 supply by 1m at most and this will not adversely effect any other circuit unless their was the unlikely scenario of faulty switch or issues with the busbar.... we are either not getting the full story or this is not what happened regardless what the OP feels was the case.... i put it to him that the DB was switched on with downstream circuits already engaged.

 

[Dizzy_Maskell]

If you switched DB 4 on at DB4's main switch and all outgoing were switched off then all you are doing is extending DB4 supply by 1m at most and this will not adversely effect any other circuit unless their was the unlikely scenario of faulty switch or issues with the busbar.... we are either not getting the full story or this is not what happened regardless what the OP feels was the case.... i put it to him that the DB was switched on with downstream circuits already engaged.

Well you would be wrong!!!!

As I think ive stated but will do to hopefully make it as simple as possible.

DB I was working on I had completed all tests and was about to begin RCBO tests.

When my colleague energised (only the busbar) of another distribution board.
At the precise moment all the RCBO in the board I was testing tripped.

 

[londonlec]

Something to do with a neutral I reckon.

 

[Richard Burns]

Could you clarify what you mean by blue phase fluctuating, you have said in post 16 that the voltage was 230V L/N on all phases.
What was fluctuating on the blue phase and how did you notice / measure it?

The fault cannot be a neutral earth fault because nothing is switching the neutral, as you have 3 pole isolators the neutral is always connected no matter what.
Energising a bus bar that has no other connections closed on it can only perhaps generate a spark as the switch closes (though it would normally be a larger spark on opening) even though there is actually no voltage reference for the spark to jump to lets assume a transient / inductive connection to earth or such.

Any fault in relation to current on the supply side of the RCD cannot cause an RCD to trip because it cannot "see" this "fault".

Therefore we are left with an interconnection of the DBs on the load side (as you say very unlikely and even then it would have to be a neutral connection which would mean that the RCBOs would never stay closed) or an electromagnetic event that is jolting the RCBOs into tripping.
Could a small spark do that? doubtful I think so I am back to a loose connection that the small spark exacerbates to cause a jolt to the RCBOs but still seems odd on a three phase arrangement.