Earth/neutral issue at DB

default · Nov 14, 2022

Today I came across an earth cable from the earth bar in the DB that went directly into the incoming neutral side of the main switch. The DB is fed from a panel that feeds other DBs and the earthing system is already TNCS. The supply to the DB does go through a rectifier but not sure why they done this with the earth. Is it OK to leave in?

DPG · Nov 14, 2022

Could you clarify the rectifier bit. And photos would be good.

default · Nov 14, 2022

DPG said:
Could you clarify the rectifier bit. And photos would be good.

It's a voltage regulator(increases voltage if there is a problem with volt drop), even though it's not required because of the length run. I'll have to get photos tomorrow.

default · Nov 15, 2022

default said:
It's a voltage regulator(increases voltage if there is a problem with volt drop), even though it's not required because of the length run. I'll have to get photos tomorrow.

[ElectriciansForums.net] Earth/neutral issue at DB

This is also one of the messiest DBs I've seen.

Julie. · Nov 15, 2022

We would need more details on the voltage regulator, if its a standard boost transformer, the earth connection would be totally wrong, it's prohibited to cross connect earth and neutral within the installation as it combines both aspects through the one conductor.

If however the voltage regulator also has isolation, then the secondary side into the cu would need a proper earth, so that connection may be valid, but perhaps inadequate.

default · Nov 15, 2022

Julie. said:
We would need more details on the voltage regulator, if its a standard boost transformer, the earth connection would be totally wrong, it's prohibited to cross connect earth and neutral within the installation as it combines both aspects through the one conductor.

If however the voltage regulator also has isolation, then the secondary side into the cu would need a proper earth, so that connection may be valid, but perhaps inadequate.

No isolation on the secondary side. Even if there was that surly that connection totally wrong.

Julie. · Nov 15, 2022

default said:
No isolation on the secondary side. Even if there was that surly that connection totally wrong.

Not necessarily, the secondary if isolated would have to have the neutral end earthed somehow, or else it would be floating (IT).

But I would expect a better more formal bond to earth than that.

As it isn't isolated, then it's totally wrong.

default · Nov 15, 2022

Julie. said:
Not necessarily, the secondary if isolated would have to have the neutral end earthed somehow, or else it would be floating (IT).

But I would expect a better more formal bond to earth than that.

As it isn't isolated, then it's totally wrong.

For future reference, if it was isolated on the secondary would you stake it. If so how far from the installation because I take it you'd have to try, and this is an old saying, be outside the equipotential zone.

Julie. · Nov 15, 2022

default said:
For future reference, if it was isolated on the secondary would you stake it. If so how far from the installation because I take it you'd have to try, and this is an old saying, be outside the equipotential zone.

Depends, really it would need proper consideration and design.

Given it's the same voltage as the overall installation I would expect a proper bond to the earth/CPC of that circuit and utilise the general earthing arrangements.

This is pretty common with 110v supplies, the isolating transformer has the secondary earthed to the earth/cpc of the primary, it's also the case for many ELV supplies where one side of the secondary, (or the -ve in the case of dc supplies) is connected to the earth/CPC of the supply.

However, there are circumstances where this may be inappropriate, then are then either isolated, or provided with a totally separate earthing system.

Some hf and audio applications come to mind.

default · Nov 15, 2022

Julie. said:
Depends, really it would need proper consideration and design.

Given it's the same voltage as the overall installation I would expect a proper bond to the earth/CPC of that circuit and utilise the general earthing arrangements.

This is pretty common with 110v supplies, the isolating transformer has the secondary earthed to the earth/cpc of the primary, it's also the case for many ELV supplies where one side of the secondary, (or the -ve in the case of dc supplies) is connected to the earth/CPC of the supply.

However, there are circumstances where this may be inappropriate, then are then either isolated, or provided with a totally separate earthing system.

Some hf and audio applications come to mind.

Thanks, much appreciated. I'll look more into this.

mainline · Nov 16, 2022

default said:
supply to the DB does go through a rectifier

DC mains ?

davesparks · Nov 16, 2022

default said:
View attachment 103728This is also one of the messiest DBs I've seen.

The incoming cables are both red which makes me wonder if the incoming supply is isolated from earth and so the link to the earth bar is required to make that pole of the supply a neutral.
In this case without the earth link you would have a 2 phase IT supply.

Yozza19 · Nov 17, 2022

One answer abstraction of electricity would put money on the neutral from the metre to that db is disconnected

default · Nov 17, 2022

davesparks said:
The incoming cables are both red which makes me wonder if the incoming supply is isolated from earth and so the link to the earth bar is required to make that pole of the supply a neutral.
In this case without the earth link you would have a 2 phase IT supply.

No the SWA is joined near the DB and it looks like they only had red.