Single pole main CB versus double pole main Cb

Electrical Fundamentals. AC power.
1

I own a house that is about 20 years old and have done quite a few renovations to the house and have had at least 3 electricians complete work on the original and renovated sections. Majority of the renovations are on 2 separate buildings from the original building.

If I look at the original external DB and main internal DB in the original building I see the main CBs on these two DBs only controls the live. In which case the neutral coming into the house is directly connected to ESKOM. All the other main CB on 3 other DB are double poled / control the live and the neutral.

I’m puzzled as to why the old main CB have not been changed. We have had a situation where Eskom switched the neutral and the live and were told that it was the cause to the damage of 2 electric gate motors (pc boards and power supplies).

Three questions:

  1. Is this single pole main CB a good idea or should it be changed to a double poled Main CB… (N & L)?
  2. Could a doubled poled CB have eliminated or gate motors being blown when Eskom switched the L & N?
  3. Will a double pole main CB eliminate our EL tripping during lightning storms? Or does anyone have an idea why this might happen?
2

Personally, I prefer 2P CB for some circuits, the big amp ones.

Then one KNOWS Pos and Neg are disconnected.

A very non-engineering view.

3

True dat. pos and neg keeps on changing which wire they come out of all the time as well. Very inconvenient.

4

After my last bout of super stupid moves with AC, the Doc last week gave it to me all the ways from Sunday, and back, of what can happen inside ones body, brain … the damage that can be caused.

I’m now so over working on AC, it is not a joke.

If I’m now forced to have to do something out of dire necessity … I phone my mate Mantashe to switch off the grid.

5

It depends on the earthing arrangement. In TN-C-S setups (you don’t have a separate earth connection from the supplier), you don’t break the neutral before the point where it is bonded to earth, since the neutral is also an earth conductor. That may explain why it wasn’t done on the “original external DB”, which I assume is the connection point for the installation. Or I could be way off too.

From that point on, SANS10142 says:

6.9.2.2 In the case of a single-phase circuit, the disconnecting device shall disconnect live and neutral. In the case of a multiphase circuit, the disconnecting device shall disconnect all the phase conductors but need not disconnect the neutral conductor in an installation connected to a supply system in which the neutral conductor is earthed direct (see the TN system in annex M).

That amendment was made in 2003.

You didn’t say if this was a three-phase setup. It if is single phase, then all current carrying conductors (live(s) and neutral) should be disconnected. But never the earth.

6

My feeling as well. Just looks more correct.

7

:laughing: I know the feeling!

8

Thank you for the clarification and yes you understood correctly.

Single phase so my feeling was correct… it just looks wrong. I will change this to comply with new regulations.

9

Agreed, but isn’t the neutral earthed at the kiosk/minisub?
Or are you referring to your building earth spike??

10

Yes, but there is also a breaker right there (in the kiosk), and for whatever reason I’ve often seen that one to be single pole in TN-C-S installations. I would think that is okay (if you left it as is), as long as there are no other loads between the kiosk and the main DB (where you isolate the whole house). The so-called “point of control” needs to isolate both live and neutral.

That’s my opinion though. I’m not a sparky.

11

Hi Richard, ESKOM have an earth spike at their pole. The singled phase then runs into the property with an earth to an outside sub DB. It’s at this point that there is a main 80A CB only isolating the live. But there are 3 other smaller CB feeding to 2 gate motors and perimeter lights. From this point the power runs into the main house to a full DB with single poll main CB & earth leakage and also to an outside building with its own full DB with doubled polled Main CB and earth leakage.

12

OK, I looked into this again, and I’m no longer certain of this. Please ask a sparky :slight_smile:

The regulations says this:

6.9.1.1 Each installation shall have one disconnecting device to disconnect the entire installation…

But it doesn’t say that disconnecting device must be double-pole. Then it says…

6.9.1.2 If an installation consist of separate parts, each part shall be controlled by a sub-main switch-disconnector to disconnect

Alright, so each sub-DB must have a way to disconnect that entire section. But again it does not say it must disconnect neutral. Then…

6.9.2.1 A neutral conductor shall not have a single-pole disconnecting device.

Alright, so if you DO decide to disconnect the neutral, it must be via a double-pole that disconnects both. Still doesn’t say you must disconnect the neutral. And then follows the part I quoted:

6.9.2.2 In the case of a single-phase circuit, the disconnecting device shall disconnect live and neutral.

But here it says CIRCUIT. Not INSTALLATION.

3.12 circuit: arrangement of conductors (see 3.15) for the purpose of carrying electric current

Not very useful at all.

3.34 electrical installation: machinery, in or on any premises, that is used for the transmission of electrical energy from a point of control

3.56 point of control: point at which a consumer can, on or in any premises, switch off the electrical installation from the electricity supplied from the point of supply

3.58 point of supply point at which a supplier supplies electricity to any premises

So to me it sounds that as long as there is some way to disconnect a consumer/load from neutral, in the sub-DB of all buildings, or at each load, you don’t need to interrupt neutral at the point of control. At least, it doesn’t seem 100% clear to me.

And if it is a three phase circuit, and neutral is directly earthed (as in all TN setups), then you don’t have to switch neutral at the load either.

13

And the earth connections in the house are bonded to the earth spike…

14

as @plonkster suggested probably safest to ask a sparky but I suspect the original/main DB in the house might have all circuits and Neutral bar wired after the Earth Leakage (my old samite DB is wired like this → the Earth Leakage specifies “usable as disconnector as per SABS” - it breaks both Live and Neutral). In this case, the Earth Leakage “device” can be used to completely disconnect the installation from the incoming supply (therefore probably satisfying 6.9.1.1-6.9.2.2).

Whereas, the CB labelled as “MAIN switch” is basically a large “on/off switch” that can be used to control the entire DB and subsequent circuits - the one that @plonkster did not quote:

6.6.1.1 Each distribution board shall be controlled by a switch-disconnector).

I don’t think a double pole CB will make any difference to the earth leakage tripping during lightning storms or protecting devices if Eskom switches live and neutral

1 Like
15

Thank you for the advice. I like to be informed when dealing with technical matters and when dealing with folk I get to do work for me.

I think you may be right about the way the main board is wired.

16

What size wiring should be used for the earth spike to DB?
My SSEG approved battery inverter recommends 10mm² :astonished:

17

Can you search for the DB earthing threads… this topic is for a different question.

18

I provided an additional earth connection from 2 inverters to an earth spike using 8mm as well as a separate 8mm earth wire to earth spike for my panels.

19

I think the rule is one size smaller than the live conductors, or 16mm^2, whichever is larger. But probably better to start a new thread for this if it turns into a longer convo.

20

Ok. I found this one which will keep me busy for a while: Let’s talk Earthing

1 Like