A Good Ground Connection

[Khun Jean]

I want to upgrade the electricty in a small shop located on the ground floor.

It has of course only the 2 wires connected with tape everywhere and somehow they even included the metal framework of the ceiling in the circuit because the metal was live.

So i took out all the wiring, sockets, switchboard and even the meter.

Now we have only the wires from the mains connection and i would like to add a good ground connection.

Hammering a piece of copper is out of the question because there is not one spot where it could be done. Concrete city....

However there is a galvanised steel pipe coming out of the ground and it is about 4 inches in diameter. It is fixed rock solid so i suspect it goes into the ground a good bit.

Through it are a few thick cables, as far as i can see it is a telehone cable. There is no transformer in sight.

Could i use the galvanised steel pipe for a ground connection?

And if so, how can i check it is any good?

[electau]

You will require a compliant main earth which will consist of a main earth conductor and electrode. The PEA/MEA require this to a minimum of 10sqmm copper and the electrode 16mm diam copper clad steel a minimum of 2.4 metres in the ground.The electrode connection should be accessible for inspection and testing, The connection should be protected from corrosion by the use of metallic paint or similar.

The main earth should be bonded to the galvanised water pipe. (equipotential bonding).

The electrode should be in a position exposed to the weather. A core hole should be drilled through the concrete for the electrode and this should be left open so as to let moisture penetrate.

If your electrical installation is MEN you will have a earth bond between the main neutral and earth. If TT there will be no bond.

All protective earth conductors from the earth terminals of socket outlets and permanently connected equipment will terminate on the earth bar of the main switchboard.

Polarity testing is required before connection to supply.

It would be recomended that all circuits be protected by RCBOs.

Metering connection and disconnection is the responsibility of the PEA/MEA.

[cooked]

Nice answer, but maybe incomprehensible to a layman? Buy a circuit breaker ( Safe-T-cut) and install as much as you can yourself. I got a hole drilled in the wall and a piece of wire attached to a nail as earthing by a Thai electrician. I was also told that the problem with my 'lectix was that I had three wires, only need two. Be careful my friend.

[Crossy]

Everything electau says is correct.

However, let's take a pragmatic view.

The pipe may well be a satisfactory ground, but you should if at all possible get a ground rod in. If you have an outside concreted area its likely to be rather thinner than indoor areas and a hole drilled through will give access to the earth for you to bash in a rod.

In the absence of a ground tester, you can do a reasonable test using a 15Watt light bulb (not a CFL) connected between your ground and the incoming live, it should light on a decent ground. Please take great care when performing this test!

Finally, as cooked suggested, you need some form of RCD. A Safe-t-Cut unit is a good solution for an existing system, but since you are doing a re-wire a split service consumer unit is neater. Have a look here http://www.crossy.co.uk/wiring/Consumer.html all the necessary parts are available from ABB (Homepro stock the kit).

[Khun Jean]

To make things even more interesting, i traced the 'mains' back to its source and it is another meter from the owners building.

So they have a meter and the little shop will have a sub meter. The group that goes to the shop has 35A written on it. I hope so. The wires are much thicker then then normal ones so it seems that at least they did that right. Previously 4 washing machines were used, so it should be enough power.

All i got are 2 wires? Can i check if the neutral wire is connected to my intended earth connection (the galvanized steel pipe)?

The plan was to wire the shop as on crossy's 'Split Service unit'.Am i allowed to connect that 'purple' wire or does someone from the electricity company has to do that.

All metal surfaces in the shop have to be grounded as some electrical equipment will be used on stainless steel worktops. Also the fridge, freezer airco etc.

[electau]

You may have a sub main from the owners metering position, the 35 A may indicate the size it may be around 6sqmm. It should be protected by an MCB to your new switchboard. Earthing. In this case in may not be advisable to use an MEN bond. But you will have to install RCD protection. The main earth in this case will run from your earth bar to the electrode and water pipe. In this case the main earth does not run from the owners main switchboard.

You should ensure that you install 3 pin socket outlets and all equipment is earthed with a 3pin plug top and 3 core flex cable. All earth conductors must be run back to the earth bar of the switchboard. Yes, you can equipotentially bond the S/S bench tops.

[Khun Jean]

Thanks, i am getting the picture although it took some time to process the info.

I changed one of Crossy's pictures to what i think i will have to do.

Can you or Crossy confirm that this is the right way. ( i not changed the amps in this picture, in my case it should not be larger than 35 total.)

Another thing i always wondered about is why appliances not have a separate live and neutral connection. Plugs can go in either way.

How is this solved in an appliance? You would think that a ELCB would trip all the time when connecting an appliance.

I understand DC and digital much better. :)

[Crossy]

The 'ELCB' in the diagram should be an RCBO. Otherwise that is a fine example of a TT consumer unit.

Most (if not all) modern appliances are polarity insensitive and don't mind which way round they are connected.

[electau]

Permanently connected electrical appliances should have the terminals marked L, N and E.

If not you must determine the neutral terminal and identify it prior to connection.

Socket outlets must switch on the L conductor. With unswitched outlets withdrawing the plug from the socket complies with this requirement.

Portable and semi portable electrical equipment supplied by a plug and socket should have double pole switching.

2 pin unpolarised plug tops are just that. 3 pin plug tops are marked and can only be inserted in a 3 pin socket outlet.

Inserting or removing a plug top of an appliance from a socket outlet will not trip the RCD device unless the appliance has an earth fault.

[Khun Jean]

Thanks electau. Fortunately i knew about which wires should be switched as i have already a few in stock. I tend to go extra safe with electricity and most of what i have are double pole.

For testing if an earth connection is any good are there measurements i can do with a digital multimeter.

I have one rated to max 700 V ac and max 20 amps.

In my condo i have one fluorescent that glows very soft while it is switched off, i checked the switch and it is the live wire that is switched(at least that is what the color black suggests) . Does that mean that the neutral is not completely neutral. What is the correct way to measure that?

[electau]

Thanks electau. Fortunately i knew about which wires should be switched as i have already a few in stock. I tend to go extra safe with electricity and most of what i have are double pole.

For testing if an earth connection is any good are there measurements i can do with a digital multimeter.

I have one rated to max 700 V ac and max 20 amps.

In my condo i have one fluorescent that glows very soft while it is switched off, i checked the switch and it is the live wire that is switched(at least that is what the color black suggests) . Does that mean that the neutral is not completely neutral. What is the correct way to measure that?

Double pole switches may be used on final sub circuits eg socket outlets but in most cases single pole are used in practice.

When using a multimeter for earth continuity testing use the lowest ohms range and a lead to measure the resistance, the lead may be 1.0sqmm min and set the meter to zero with the lead connected. Earth measurements are taken from the earth electrode connection to the earth bar of the switchboard and then to all point of the installation that are earthed. This should be less than 2 ohms, in practice far less. (The resistance of 2.5sqmm conductor is 0.008 ohms per metre). When measuring supply voltage use the highest AC range. Do NOT use the current ranges.

It would appear that the fluor light fitting is switched on the neutral instead of the line, a common defect, potentially hazardous as the lampholders are live when switched off. Reversing the L and N connections at the fitting will solve this problem. The polarity can be checked using a neon test pencil. Black should be L and N should be white or grey but they could have been reversed at a switch somewhere else on the lighting circuit.

It is not practical to measure the electrode to soil resistance with out specialised equipment.

If the electrode is at the required depth and is equipotentially bonded to the water pipe this requirement will be satisfied.

Edited October 17, 2012 by electau

[Pib]

However there is a galvanised steel pipe coming out of the ground and it is about 4 inches in diameter. It is fixed rock solid so i suspect it goes into the ground a good bit.

The steel pipe probably does run a good distance underground, but as the same time it could be connected to same size PVC piping/tubing just under the concrete or using PVC connectors to join pieces of the steel pipe...either way, the grounding continuity would be broken by the PVC inserts possibly creating an unsatisfactory electrical ground.

[electau]

However there is a galvanised steel pipe coming out of the ground and it is about 4 inches in diameter. It is fixed rock solid so i suspect it goes into the ground a good bit.

The steel pipe probably does run a good distance underground, but as the same time it could be connected to same size PVC piping/tubing just under the concrete or using PVC connectors to join pieces of the steel pipe...either way, the grounding continuity would be broken by the PVC inserts possibly creating an unsatisfactory electrical ground.

This is why an earth electrode is used, the water pipe is bonded to the main earth (equipotential bonding).

Edited October 20, 2012 by electau

[doglover]

Scenario on topic. New home construction. Home water main fed from well (or could be from village supply). Typical install of water piping would be pvc. Would there be any value in adding a galvanized steel section to the piping and bonding it to the ground electrode?

[electau]

Scenario on topic. New home construction. Home water main fed from well (or could be from village supply). Typical install of water piping would be pvc. Would there be any value in adding a galvanized steel section to the piping and bonding it to the ground electrode?

Conductive water piping. Conductive water piping that is both:

1. Installed and accessible within the building containing the electrical installation; and 2. Continuously conductive from inside the building to a point of contact with the ground, shall be bonded to the earthing system of the electrical installation.

Equipotential bonding is intended to minimise the risks associated with the occurance of voltage differences between exposed conductive parts of electrical equipment and extraneous conductive parts.

Note. An isolated section of metallic piping that does not meet the above requirements would not be required to be bonded to the main earth.

[Crossy]

Scenario on topic. New home construction. Home water main fed from well (or could be from village supply). Typical install of water piping would be pvc. Would there be any value in adding a galvanized steel section to the piping and bonding it to the ground electrode?

Nope, it may slightly improve your overall ground impedance but I would not install solely for this purpose. You can do better by bonding your structural steel to the rod.