2-Pole Isolator Switch (Din Rail) Won't Stay Up

[Sidewinder]

Mikron,

You do realise that you are personally legally both responsible & liable for the work you have done.

I appreciate that you have misunderstood, however, in this case you should not have taken the work on if you did not fully understand the situation, which it is patently true from your posts you did not.

You have changed the protection characteristics of the circuit protection it seems, without any verification if this is still suitable.

Should the property burn down, or someone get killed, then you as the "last man standing" as it were, will be liable, and the insurer will be looking for someone to blame, and get their money from, that will be you, unless you can prove your competence and the "process" that you went through was in accordance with industry practice to do this work.

It seems that you  could have left yourself wide open here, and could also have put lives & property in danger.

 

[OnOff]

Without proper testing of the circuit in question you could still have a situation there where the new D curve breaker is "holding" OK whereas a C curve as was fitted would still trip and was tripping with good reason.

 

[SBS Dave]

Have just read the whole thread and I would have guessed it was a 2-pole MCB and not a switch.

I have had first hand experience of this type of application in Ethiopia, where it is common practice to have an upfront MCB.

Most domestic supplies are overhead ones, with the main fuse mounted on the pole, to protect the supply cable to the dwelling.

Network capacity is limited, with supply disruption occurring 3 or 4 times per day. A 40A or 50A 2-pole MCB is therefore used as an isolator and also as a load limiter, to prevent overload of the network. 

A lot of devices are rated at 4500A ssc, because Ze's are usually fairly high and in fact the cpc is usually the same size as the line conductors, in order to achieve as low a Zs as possible.

Ethiopia has now adopted BS7671 16th Edition and now tend to use an upfront 2-pole RCBO on modern properties. This still provides load limitation and also provides shock protection. Nuisance trip is not an issue in Ethiopia, as they are used to the power going off on a frequent basis.

SBS Dave

 

[ProDave]

I wonder if the OP will come back and tell us if he's in the UK, if not where is he?

 

[Sidewinder]

I often use a 2 pole MCB to protect a 1ph sub main, don't know what is so odd about it TBH?

My concern is the OP being so unsure and leaving themselves at such a risk!

 

[batty]

It certainly sounds like he is not in this country. Very worrying and a shame he has not given more information.

 

[Blue Duck]

Not in the UK given terminology used and some literal translations? Wheres Marvo?

Also does anyone recognise those brands? fake merlin gerin  :Blushing

Scoobed SBS Dave for the explanation of Ethiopian Electrics

 

[Mikron]

Thank you again guys.
 
 
In my original post, I omitted info not pertinent to the basic question - as I am told posts that are too wordy can be a deterrent to viewers reading them. However, it sounds like you need that info now.
 
 
I was doing this as a DIY job just to help out friends before their imminent move back to the UK (we are in Cyprus).
I recommended my friends get a Cyprus-registered electrician in if the problem recurs.
 
The intermittency of the fault does not help, of course; nor its apparent lack of correlation with anything.
However, all the circuits served by the CU have MCBs (C6, C16, C32), and none of those ever trip (and they are all mechanically free to do so). That was my first pointer to the fault possibly being with the incomer itself. Could there have been a LE fault between the incomer and the MCBs? -No; there's just the short tabbed line busbar in fresh air, and the RCD in the meter box would have caught it. The RCD in the meter box would also have caught any earth faults in individual circuits. Also, the neutral lead out from the incomer is well separated from the line busbar, so a short-circuit there is not possible.
I think that logic still holds true now I understand the incomer is actually an MCB.
Could individual currents through several MCBs have combined to exceed the incomer (MCB)'s rating? Yes, but that would be quite some coincidence. And the fault often occurred when 'just a couple of lights were on'.
 
Other info:
- I checked the current through the incomer with all lights, sockets and appliances switched off: 0.009A. That is, there was nothing draining current that they were not aware of, at least not on a permanent basis; just a background trickle.
- About a third of the terminals I checked (in the CU and in sockets) were slack (often the case here in Cyprus) ; now tightened.
- The tabbed busbar itself is OK now, though there was an area of pitting/carbonizing on the tab connecting to the incomer, which made me suspect arcing and a poorly tightened terminal.
- I don't have a Megger/equivalent to check earth loop impedance, but it is not looking like an earth fault since the RCD never trips.
- The CU as a whole is served by devices in the CUs upstream of it, providing some protection, albeit with the risk of nuisance tripping in unrelated buildings on the property.
- To 'onoff': the 'D curve breaker' was only temporary.
- My own house, new a few years ago, had the electrics done by a Cypriot electrician I presume and it would have been inspected before the building permit was issued. They installed an MCB as the incomer.
 
To recap:
? earth fault                    no               RCD never trips
? overcurrent fault          unlikely        individual MCBs never trip, neutral well separated from line busbar
? incomer fault               possible
 
All in all, replacing the incomer seemed a reasonable starting point. If it appeared to fix the problem, good; if not, it might force the problem to show itself on a protection device on a particular circuit.
 
To 'SBS Dave': that Ethiopia info is interesting; certainly some parallels here.
 
I appreciate your concerns and comments, one and all.
I hope this last post goes a little way to reassure you that I did apply some thought to my actions.

 

[ProDave]

The incommer RCD will trip on the SUM of the current being drawn by ALL circuits.

The fact that no individual circuit trips just shows that no individual circuit is overloaded, but the total current in uses could exceed the rating of the incomer and cause it to trip.

You need to adjust your energy use, and avoid using several large appliances at the same time.

I doubt it is tripping due to a "fault"

 

[Mikron]

ProDave,

Thanks. I appreciate the cumulative loading issue, hence my writing:

Could individual currents through several MCBs have combined to exceed the incomer (MCB)'s rating? Yes, but that would be quite some coincidence. And the fault often occurred when 'just a couple of lights were on'.

Also, they can have the cooker, hob, imm.htr on at the same time without tripping; and the other circuits serve only a few lower-power devices such as lights, TV, computer, etc. They have not tried switching absolutely everything on at the same time, but that would probably trip one MCB or another due to exceeding the diversity factor.

 

[SLIPSHOD & SLAPDASH]

During a chat with a Greek friend last summer he was telling me they are charged 'back home' (meaning Cyprus) on their maximum demand. In their holiday home they have gone for a cheaper tariff (he could not remember the maximum Amps) so they could only run the washing machine or the dishwasher or the air con but none together. It sounded like its as low as 16 or 20A . This may explain the breaker as a main switch either as a supply requirement or for the customers own benefit  to stop them drawing too much.

 

[Mikron]

SLIPSHOD AND SLAPDASH, 

That's an interesting angle!

I have not heard of such a basis for charging. The electricity authority here in Cyprus sets a maximum current for a property, and that is reflected in the trip-current setting on the main breaker in the meter box (mine is 30A, 3-phase). Some old properties do not have such a breaker - maybe that's where it becomes necessary to be careful not to draw more than the designated current (like an unarranged overdraft at the bank, with associated fees).

 

[Doc Hudson]

Thank you again guys.
 
In my original post, I omitted info not pertinent to the basic question - as I am told posts that are too wordy can be a deterrent to viewers reading them.

Whilst you are correct that long rambling posts can be off putting and now the thread has got a bit more context to it, it is moving along nicely.  I will just comment that the initial post would have been better with a few more key facts included such as: The type of installation, The location of the installation if non-UK and your experience or background. Terminology can vary between DIY/Trade, UK/Non-UK, and this can confuse the issue when members are trying to give accurate replies. Some of the early replies reflect this  and its not until post#17 that the discussion has actually got going in the right direction. So for future questions if all members can include a bit of context to installation this would help everyone, Thank you.

Doc H.

 

[Mikron]

Doc H - Guidance noted, thanks.