What is meant by 'earthing' a piece of equipment?

Question

We have a large fridge unit at work. The compressor unit is mounted remotely in a steel cradle away from the fridge. I am told this should be earthed.
Am I right in saying that an earth cable should be attatched to the steel cradle and the other end of the cable bolted to a gas or water pipe that enters the ground?

Answer 1

Get a professional to do this!!!

Sorry, I'm sure this is not what you wanted to hear (extra expense etc.), but there are allsorts of rules and regulations in every country concerning the earthing of equipment. If you don't follow them and someone was to get electrocuted (even yourself), then you are wide-open to allsorts of fines and penalties. Your insurance company may even refuse to pay and in some countries, you may even face jail time.

You are right that it needs connection to some piece of metal in the ground that has a sufficient surface area that it will have a very small resistance passing current into the Earth. There are special meters for measuring this and certainly in Britain (where I am), it needs to be measured by a qualified electrician to be covered by insurance. Also the gas AND water pipes need to be earthed to each other (called cross-bonding) as so many pipes are being replaced with plastic ones now, that it is considered safer to have this "double earth".

I hope this helps - Sorry 'bout the bad news though, but it's better than a massive lawsuit I suppose... Let your electrician pay the insurance bill if something goes wrong!

Answer 2

Earthing a piece of equipment means connecting it electrically to the "mass of the Earth".
At the supply sub-station the transformers are arranged such that the electrical "neutral" line is bonded to a bloody great metal mesh or plate sunk into the ground. Thus at your premises the neutral line "may" be at the same potential (don't trust that assumption and touch it to test, it could be dangerous. For many reasons the Neutral could be quite a lot of volts away from "earth" potential).

The "Live" or "line" conductor will be 230V from Neutral (give or take some). Normally the current flow is sub-station through live, through appliance, and back to sub-station through neutral.

If a fault develops in your fridge and the casing becomes "live" the electrical flow will be through the case and down to the Earth - and then through the ground back to the sub-station to complete the circuit. This will also blow your fuse or trip the circuit breaker.

It is the case that all exposed pipework and metalwork should be connected together by connectons at Earth potential but that is not for them to provide the sole Earth source.

NEVER connect an appliance to a water or gas pipe as your Earth conductor. This is because you do not know what the pipe is made of under ground and you do not know what the ground is like that the pipe passes through. To do so is illegal under the building and wiring regulations.

ALWAYS use a properly provided and bonded Earthing point. This may be at the incoming meter or may be a properly installed Earthing spike outside the premises.

If in doubt you must get a qualified electrician or your insurance, life and criminal record may at risk.

Answer 3

You are quite right. The unit should be earthed. This should have been done when it was installed.
And yes, you can connect it up to the water pipe installation. Thats what is usually done. noone puts in an extra earth spear for the sake of grounding one unit. But make sure to use the right square lead. This should be green/yellow.

It is dangerous to run this fridge when its not grounded!!!! Someone might get killed in case of a earth fault on the unit. Even if the fridge is some distance away from the compressor unit. Let an electrician do the job.

Answer 4

Earthing is British for grounding. I would never us a gas line for ground. Besides the possibility of catastrophic failure should something go horribly wrong, besides the fact that it's contrary to most building codes, gas lines are usually made of steel pipe which has been coated with tar and wrapped with Kraft paper. Gas lines are a piss-poor ground! Water lines these days are usually made of PVC plastic or, if metal, have an insulating section to prevent galvanic corrosion. Also a piss-poor ground.

Frankly, I'd connect the steel cradle to the power system's safety ground. In the USA this is usually a solid green, or yellow with a green stripe. The safety ground is a non-energized conductor that eventually connects to the ground stake where power enters the building. It only conducts current if a fault develops in the motor, but then it's essential for safety (both fire and electrocution.) That's how a professional electrician would do it.

Answer 5

Earthing equipment means intentionally creating the easiest possible route for electrical current from components of the equipment that should not normally be 'live' with electricity (usually the casing or any other part that comes into contact with a person) to the ground, the intention being that if this part of the equipment does become live with electricity, the 'earthing' has the two following effects.
Firstly, any electrical current will travel through the 'earthing' wire instead of through any person touching the equipment (as the earthing wire offers less resistance to the flow of electricity), minimising any risk of electrocution. Also, as the earthing route offers very little resistance to the flow of electricity, as soon as the 'earthed' part of the equipment becomes 'live' with electricity a surge in electrical current occurs from the supply (the wall plug), through the equipment and down to earth. This has the intended effect of blowing the fuse of the equipment or the supply cutting all electrical supply to the faulty location.
With regard to whether your equipment should be earthed... YES!!! Otherwise if such a fault occurs and the steel cradle becomes live with electricity - the supply will remain and will travel to earth through the first person that touches it, provided that their feet are on the floor - not to be recommended.
As for how to connect the earth cable, it needs to be connected to any conductor that travels into the ground as long as that conductor is safe to have electricity travelling through (not a gas pipe!). I would recommend you get someone qualified to do this for you because of the potential consequences of getting it wrong. Hope this is easy to follow and helps!

Answer 6

earthing is another way of saying grounded. depending on the electrical code in your area, grounding to a water pipe may be legal, but i would attach it to the electrical ground (bare copper or green in the cable coming into the fridge) instead. metal conduits SHOULD be ground as well. if you were to attach it to the water pipes, there is a small chance that the current going through it in a ground fault situation may be able to find another shorter path to ground than the pipe, making a dangerous situation for anyone who happend to be touching the pipe and the actual ground at the same time.

Answer 7

Yeh that would do but I wouldn't earth it to a gas pipe.Maybe just get a steel rod and hit ti firmly into the ground would be better

Answer 8

You are mostly right. Earthing means it needs to be grounded. Personally, I dont recommend the method you mention (tying onto a gas or water, especially gas). It should have its own ground to protect the equipment best.

Answer 9

I think the other end just needs to be grounded - ie to steel work going into the ground, water would be better than gas for obvious reasons. Basically it diverts all the current should there be a electrical fault.

Answer 10

It needs to be at the same earth potential as the mains (earth) supply to the fridge. The best way is to earth it to the main earth rail in the supply DB or a convenient point common to that.