Corroded swa gland - garage CU

[Leyland30]

Hi,

Have a garage consumer unit supplied from the house CU via a 6mm 2core swa. I noticed this morning the gland entering the garage CU was loose so opened it up to tighten up the gland lock nut. Unfortunately it appears the gland as it enters the garage cu has corroded and brocken away from the lock nut. It's only been install 3 years and the other glands show no sign of corrosion. I have suspicions as to what has caused it but would like some other views on the matter. Pics attached. Thanks

 

[telectrix]

No I mean isn't that tail isolated from the earth bar? I don't see any electrical connection between the enclosure and the earth bar
.

that might be the problem. causing (possibly leakage) current to flow through the enclosure. clutching at straws here, just thinking aloud.

 

[Richard Burns]

No I mean isn't that tail isolated from the earth bar? I don't see any electrical connection between the enclosure and the earth bar
.

The main earth is inappropriately connected to the mounting screw holding the earth bar retaining strip to the body of the CU, however there is a metal connecting plate from the mounting screw to the earth bar, you can just see it entering the left most earth terminal, so there is earth continuity between all points (except the armour of the incomer!)

 

[Marvo]

What a lash up of an installation!

It looks like there is a bit of corrosion around the other two glands at the bottom, and if it is non-ferrous then I'd guess that there's a quantity of aluminium in the alloy which has led to galvanic corrosion.

It looks like the paint was cleaned off or maybe flaked away when the nuts were tightened, I can't see corrosion though.

Completely agree that whole enclosure is a dogs breakfast. Never ceases to amaze me that even with the right tools and decent materials you could end up with such a poor quality installation.

 

[Leyland30]

I got time last night (before Poldark) to swop out the gland and investigate the damage. As Marvo suggested, moisture has been entering the CU through the supply cable SWA; rain water appears to be entering the SWA via a degraded external joint box, this is then compounded by the use of a sealed outdoor gland which is preventing moisture escaping. The moisture ingress appears to have caused the steel locknut on the gland to corrode and expand resulting in mechanical failure of the gland body as it passes through the CU casing.

There is no evidence of corrosion to the CU casing or gland body. Provisional checks suggest water hasn't entered L N flex within the SWA, I need to do a full insulation test to establish this fully.

Westwood, I have replaced the CPDs with compatible Schneider type.

Richard, the other glands are future spare capacity - earth bonds will be provided when they are utilised.

DaveSparks - outrageous!

Marvo - jees, tell it how it is.

Thanks again

 

[Leyland30]

Richard, can you clarify what is inappropriate regards the earth connection.

The main earth is inappropriately connected to the mounting screw holding the earth bar retaining strip to the body of the CU, however there is a metal connecting plate from the mounting screw to the earth bar, you can just see it entering the left most earth terminal, so there is earth continuity between all points (except the armour of the incomer!)

 

[Wilko]

Richard, can you clarify what is inappropriate regards the earth connection.

I'd prefer to not have plastic sandwiched there, if I see correctly. The plastic will deform over time and the earth nut will lose its tension. The earth should be directly to the box, IMHO

 

[freddo]

however there is a metal connecting plate from the mounting screw to the earth bar, you can just see it entering the left most earth terminal, so there is earth continuity between all points (except the armour of the incomer!)

Well spotted, I only looked at the tops of the terminals!

 

[Richard Burns]

Good to hear feedback about the fault, thank you.

Richard, can you clarify what is inappropriate regards the earth connection.

The fixing for the earth and neutral bar support is not intended for use as an earth connection for another cable and making changes to this connection could cause a loss of earth continuity to the body of the CU. The ring crimp that has been used appears to have been either closed down or cut down in order to fit into the space, which could limit the effectiveness of the connection.
In all likelihood the connection is fine but it just has the potential to cause problems and fitting it directly into the earth bar would reduce the risk.

 

[Leyland30]

Following comments regards MCB compatibility and earth terminations, Schneider CPDs have been replaced with BG ones - the incoming isolator and earth was over complicating matters so these have been removed.

Picture courtesy: professional-electrician.com

God bless and sweet dreams.

 

[Dave OCD]

Now that board is very scary !

 

[freddo]

Took me a while to work out how the gland was fitted to the enclosure! Good job it isn't a metal clad CU.