explanation of main earth bonding?

[Kev2632]

Hello, could anybody explain why Main earth bonding is required and how it works in an event of a fault?

 

[Kev2632]

does this sound right????



The reason the water and gas pipes are bonded is to allow any fault current to flow through them as well, for the duration of the fault, thus raising the potential or voltage of the pipes to the same as the metallic appliance under fault. This may sound a bit mad but if you are touching a metal light switch under fault and happen to be touching a metal tap then the two voltages will be equal, or at least within 50V of each other, which is considered safe.

As Micheal Faraday demonstrated in the 1850's if there is no potential difference (different voltages) then there can be no electron flow and therefore no current. You don't get a shock.

Without the equipotential bonding the pipes would be at 0V as they are connected directly to the general mass of earth (GMA) so you would receive a shock

 

[simplespark]

Yep that pretty much covers it.

 

[simplespark]

If it helps, I use Geoffrey Stokes' example from guidance note 8, which suggests limiting electrical current flowing in a person who is simultaneously connected between an exposed and extraneous conductive part to 10mA, when deciding to provide main equipotential bonding or not. Some people will argue against this because IEC 479 shows that, in most people, the human body can withstand the physiological effects of 30mA of current for 0.4s, and where all circuits can be proven to disconnect in 0.4s or less (typically 0.1s where type B Mcb's are used)

 

[roukel01]

And then a plumber comes along and sticks a load of Plastic joints everywhere without telling anyone!

 

[Edd]

The main bonding remains at 0v (to the surroundings) and we try to get all metalwork and accessories to the same 0v potential hence the word "equal potential bonding"(equipotential bonding)with an appliance/ accessory under fault that current is pulled down to 0v not raised.. but I may have miss read (and i often do)

 

[ackbarthestar]

MPB is not just for fault currents on final circuits but where PME systems are installed it protects the installation from DNOs circulating fault currents where the PME neutral has either gone open circuit of high resistance

 

[Chr!s]

does this sound right????



The reason the water and gas pipes are bonded is to allow any fault current to flow through them as well, for the duration of the fault, thus raising the potential or voltage of the pipes to the same as the metallic appliance under fault. This may sound a bit mad but if you are touching a metal light switch under fault and happen to be touching a metal tap then the two voltages will be equal, or at least within 50V of each other, which is considered safe.

You would normally assume no fault current flowing when calculating, though in the real world that's no the case. The bonding transfers potential to the exposed conductive parts, reducing the touch voltage. The 50 V is considered to be relatively sake though bonding alone may not achieve a 50V touch voltage, it may be considerably higher.

As Micheal Faraday demonstrated in the 1850's if there is no potential difference (different voltages) then there can be no electron flow and therefore no current. You don't get a shock.

Without the equipotential bonding the pipes would be at 0V as they are connected directly to the general mass of earth (GMA) so you would receive a shock

The voltage Maybe much higher

Regards Chris

 

[SirKit Breaker]

Hello, could anybody explain why Main earth bonding is required and how it works in an event of a fault?

Hi mate, i personally have no issues with the question that you have asked, for whatever reason you have asked it, But can i ask you the reason why you asked it?

Are you just curious? an Apprentice? or a DIYer who wants some understanding. I have only brought this up because unfortunately some amongst us take great pleasure in belittling posts of a similar nature. I have seen poor souls on here shot apart for asking similar questions (not something i condone) because those who do know better expect everyone else to also know, or think that just because it is an Electricians forum, no one else is allowed in.

Cheers.............Howard

 

[Kev2632]

Hi mate, i personally have no issues with the question that you have asked, for whatever reason you have asked it, But can i ask you the reason why you asked it?

Are you just curious? an Apprentice? or a DIYer who wants some understanding. I have only brought this up because unfortunately some amongst us take great pleasure in belittling posts of a similar nature. I have seen poor souls on here shot apart for asking similar questions (not something i condone) because those who do know better expect everyone else to also know, or think that just because it is an Electricians forum, no one else is allowed in.

Cheers.............Howard

Just Curious lad,

so basically we aim to make the Main water and gas the same potential as the rest of equipment in the house is that correct yea?

 

[grimysparks80]

I used to try and explain it properly to customers, but there are only so many hours in a day. Now all they get is `Ive got to earth your pipes luv`.lol.

 

[i=p/u]

i naaturally started to explain the ins and outs , but not no more......

 

[SirKit Breaker]

Just Curious lad,

so basically we aim to make the Main water and gas the same potential as the rest of equipment in the house is that correct yea?

There are several reasons for bonding exposed metalwork to earth. It reduces the resistance of the fault current path, it helps to ensure that the bonded pipework will not stay live for long in the event of a fault which may come into contact with the pipework, such as cables under floors etc which could chaff through if they are touching pipework, or DIY charlie does something stupid, and in a TNCS installation it is essential that bonding is in place in case of failure of the neutral connection.

Cheers..........Howard

 

[Deleted member 9648]

Electricity will always flow to earth given the chance. In the event of a fault between a live conductor and a conductive part...(earthed metalwork which is part of the electrical system)...there may be a rise in voltage between conductive parts and the general mass of earth until the protective device clears the fault.
Anyone in contact with a conductive part for the duration of the fault may be at risk of a shock. In practice the risk is minimal,as the person is likely to be insulated from the general mass of earth by virtue of being in an insulated environment...(wooden floors,dry concrete,carpet etc.
A problem arises because incoming metallic services...(extraneous conductive parts).. introduce the general mass of earth into this insulated environment....now anyone in contact with a conductive part and ECP for the duration of the fault will recieve a serious shock. By bonding ECP's to CP's there can be no potential difference between them and the shock risk is minimised.
This explains why bonding is carried out at the point of entry to the building,because the hazard is coming from outside......once within the building the ECP is unlikely to regain an earth potential,so it matters not how many plastic inserts a plumber installs,there is no need for continuity,the problem has already been dealt with.
This is the ONLY reason for main bonding....effects such as preventing pipes from becoming live in the event of them contacting a live cable...reducing Z through parallel paths...etc etc are by products of bonding,not the reason for it.

 

[Chr!s]

Electricity will always flow to earth given the chance. In the event of a fault between a live conductor and a conductive part...(earthed metalwork which is part of the electrical system)...there may be a rise in voltage between conductive parts and the general mass of earth until the protective device clears the fault.
Anyone in contact with a conductive part for the duration of the fault may be at risk of a shock. In practice the risk is minimal,as the person is likely to be insulated from the general mass of earth by virtue of being in an insulated environment...(wooden floors,dry concrete,carpet etc.
A problem arises because incoming metallic services...(extraneous conductive parts).. introduce the general mass of earth into this insulated environment....now anyone in contact with a conductive part and ECP for the duration of the fault will recieve a serious shock. By bonding ECP's to CP's there can be no potential difference between them and the shock risk is minimised.
This explains why bonding is carried out at the point of entry to the building,because the hazard is coming from outside......once within the building the ECP is unlikely to regain an earth potential,so it matters not how many plastic inserts a plumber installs,there is no need for continuity,the problem has already been dealt with.
This is the ONLY reason for main bonding....effects such as preventing pipes from becoming live in the event of them contacting a live cable...reducing Z through parallel paths...etc etc are by products of bonding,not the reason for it.

There may be a substantial potential difference.