Incomer switch

[mr_chaela]

Hello,
My premises has a 3 phase supply fed from the next door council depot. Problem is that any electrical faults cause a trip in the depot which is inconvenient after depot working hours. I had the depot electrician look into it and he recommended a change of the incomer switch on my distribution board.
My distribution board is a Bill Talisman Plus with a 100A T13SD 3 pole incomer. What can I replace this with so that this trips rather than the one in the depot.

 

[mfarrow]

You'll need to find out what breaker it is that trips in the depot. The switch you have shown is a basic isolator (switch).

Some photos would be handy.

 

[Taylortwocities]

Please post pictures so they appear in your replies.

Its easy.

Read how to do it here: //www.diynot.com/forums/viewtopic.php?t=129539

 

[ricicle]

Just changing the incoming switch on your DB will not necessarily stop trips in the council depot DB unless some alterations are done in there as well.
Pictures of both DB positions would be good as TTC said.

 

[mr_chaela]

Thanks for the prompt replies, here's the pics as requested:

Depot Trip. Is a Hager CN484U 100A, 100mA trip RCCB

Depot Trip

• mr_chaela
• 11 Jan 2012
• 1

Main DB, Incomer is Bill Talisman 100A T13SD

Main DB

• mr_chaela
• 11 Jan 2012
• 1

The R/H armoured cable is fed from the lower 3 breakers on the R/H bank and feeds...

Hall DB. Incommer is Proteus 100S3 AC22b

Hall DB

• mr_chaela
• 11 Jan 2012
• 1

Also fed from the Main DB (can't remember which set of breakers) is...
Lower Grnd DB. Incomer is MK LN5780 80A 2 pole 30mA trip

Lower Grnd DB

• mr_chaela
• 11 Jan 2012
• 1

Activation of this test button does not affect Depot Trip

The ideal solution would be to separate the 3 DB's, all with appropriately rated RCCB's such that they are 3 independant zones but I don't know if this is possible without spending too much money - the premises are used by a youth charity who have to raise their own funds to survive.

 

[ban-all-sheds]

Unfortunately lack of money does not exempt the charity from legal obligations such as those in the Electricity At Work Regulations, any Local Authority licensing requirements, public liability issues....

You need to get an electrician.

 

[mr_chaela]

Getting an electrician is not a problem, the current (no pun intended) setup is obviously not satisfactory, although its apparently been like this for some years, I would just like to know what is possible in the most cost effective way.
One local electrician looked at it and said 'Yeh, you gotta change all the MCB's for RCBO's and that's gonna cost ya'
That's why I'm on here, looking for alternatives and hopefully a cost effective compromise.

 

[toptip123]

Is the rating on the rcd in the other unit 100mA trip?
If so you could fit a 3 phase 30mA RCD to the main incoming tails. or swop the main switch in the bill board for 30mA RCD from EATON/MEM.

The armored cables aren't made off well if the armorings are not connected properly you may not have an earth in some parts of the installation......

 

[bernardgreen]

I have had a similar problem in the cottage I bought in June. The supply came from the adjacent shop's meter which was once part of the cottage. I had to become a keyholder of the shop to be able to reset trips. My only solution was to get a new supply to the cottage ( less than £1000 in my case ) as the shop supply was TT and had to have an RCD on the incoming supply and the DNO could not give me a supply direct from the incomer with out an RCD in the shop.

Provided the supply to the depot is not TT then you could ask for your supply to the taken from the incomer before the RCD so only your RCD trips.

If the depot allow this ( and maybe pay for it ) then they gain the benefit that an electrical fault in your property will not trip off the depot's supply which could be inconvenient to them, especially if it happens when your property is closed and locked.

 

[bernardgreen]

Putting a 30 mA RCD in your premises will not ensure that the RCD in the depot will not trip on a fault in your premises. It will reduce the chances but not eliminate them. It is possible that when your RCD opens on a 30 mA fault the action of opening 3 phases creates a transient "disturbance" that the 100 mA RCD in the depot may react to and open. The mechanism is that the "disturbance" as the phases disconnect creates capacitively coupled earth leakage currents. The more wiring there is ( more phase to CPC capacitance ) the more likely that both RCDs will trip.

 

[mr_chaela]

Thanks for the replies,
The RCD in the council depot is rated at 100mA.
I'm not sure (didn't think to look) if the depot supply is TT but they insist on the RCD at their end to protect the underground cable to our premises (which we lease from the council) and they will not allow us to become keyholders.
When you talk about the amount of wiring, is this the overall amount or the length of underground to the depot, I reckon the underground cable is about 70 - 100 metres long.
The board on the lower ground floor has 30mA trip on a single phase from our main board and that does not affect the depot trip.

 

[Adam_151]

If the Supply is TN and the loop impedance is in spec (and if not, why not), then an RCD to the buried cable is not required, the cable is protected by the fact that its SWA and any digger bucket, etc that goes through it, will contact the armour first before any phase and ensure that a fault to earth is created the fuses are cleared.

If they however insist on having some RCD, then you could perhaps try and persaude them to swap it for a time delayed type (either 100mA as the present one is, or even better, 300mA), then at your end 30mA main incommer, this should be sufficent to acheive discrimination although not the nice-ist set up in the world

 

[bernardgreen]

When you talk about the amount of wiring, is this the overall amount

The wiring to lights, switches and sockets etc after the CU.

 

[mr_chaela]

How does this sound as a plan of action:

We get our incomer changed to a 30mA RCD.
Toptip123 suggested an RCD from EATON/MEM as a direct replacement for the Bill Talisman T13SD - is this the one, Eaton MEM EBMR30 Memshield3 3 Module TPSN Residual Current Device RCD 100A 30mA (incomer kit). Found this for £110.57 inc VAT & delivery.

If this does not completely solve the problem then we persuade the Council Depot to change the RCD at their end to a 300mA delayed type as suggested by Adam_151.

From my point of view this would be the cost effective compromise I've been looking for, what do you think?

 

[ricicle]

It will also be a risk fitting a 30mA RCD as your incomer due to the number of circuits on the TP board increasing the possibility of nuisance trips (but will probably be more convenient than your existing situation)
It is definitely a job for a good electrician - with industrial experience, not just a chancer.