G
GMjohn
Hi, I'm new to the forums so am not sure if this is the right section for these questions, but it appears to be a good area to place them.
I'm pretty new to learning about electrical installation, and as i go along, i realise there's still some gaps in my understanding which I can't seem to find clear satisfactory answers in the regs, text books or on the internet. So I thought I'd join up and ask what many experienced electricians will probably consider obvious and stupid little questions, but I'll never develop the deeper understanding of things that I want if I don't ask. Maybe it will also help other learners in the same boat as me.
I find the subject of earthing and bonding in bathrooms to be a source of confusion. I can't fully understand the actual situation with bathrooms and earth potential, and what the underlying principles are behind it.
I understand about it being a higher shock hazard due to the bare feet and wet conditions lowering bodily resistance, but don't have a good grasp of how this affects the earthing issue and some of the advice I have seen.
To illustrate, in the last few months I've come across quite a few installations where the wiring has been different.
For example, a bathroom with 4 230v light fittings where the supply went into a junction box and all the cables radiating out of this to the fittings had the cpc cut off at both ends so each cable had no cpc continuity. Is this correct? Wouldn't it have been better to have had cpc continuity down every cable going to the fittings, and just not terminate the cpc at the fitting, or is it normal and to regulation for these cables in the bathroom ceiling to not have cpc continuity down them?
I guess I'm asking is it correct to cut off the cpc at the bathroom entrance and have no cpc continuity going through any cable run in the ceiling to bathroom fittings, or should there be cpc continuity in these cables going around the bathroom ceiling even if there is to be no termination at the actual fitting?
Same when dealing with low voltage downlights. Every installation i've seen had a junction box at each fitting which fed a single transformer for each light. The cpc was not taken down to the light fitting on any installation, but on one installation I've seen the cpc cut off at both ends of all the cables so there's no earth continuity at all between the cables running from junction box to junction box in the ceiling. In other installations I've seen the cpc terminated at each junction box so the cables in the bathroom ceiling do have continuity. Which is the correct way, or is either acceptable?
I came across a bathroom the other week which had a 230v wall and ceiling light, both with exposed conductive parts which had earth continuity when tested. The ceiling light fitting had a single cpc conductor being run separately to a junction box in the loft as the light fitting wiring only had line and neutral conductors. Is this correct, or did the person who installed it do something wrong by introducing this earth continuity into the bathroom fittings?
I see it mentioned about not introducing earth potential into bathrooms, yet also see supplementary bonding being a necessity under certain conditions, which then introduces earth potential into these areas. I just don't fully understand the underlying principles behind these rules. If its better to keep earth potential out of bathrooms, why have this bonding?
If it's ok and safe to keep earth potential out of bathrooms, why allow earth potential into other areas of the house?
I'm obviously getting mixed up on this subject. I understand the general principle of equipotential bonding and earthing ensuring that exposed and extraneous conductive parts remain at the same potential so no current will flow if two different parts are touched. But if it is safer for that reason, why shouldn't exposed conductive parts in bathrooms be earthed, yet extraneous conductive parts should be? Won't they be at different potentials? Is it something to do with water spray and conductivity?
As you can see I am a little confused. No amount of reading or sources I find give me a satisfactory understanding. Can anyone help by answering these questions or pointing me to a good resource on the subject? I appreciate these may sound like stupid questions, but my lack of clarity on the matter has been bothering me for a while.
I'm pretty new to learning about electrical installation, and as i go along, i realise there's still some gaps in my understanding which I can't seem to find clear satisfactory answers in the regs, text books or on the internet. So I thought I'd join up and ask what many experienced electricians will probably consider obvious and stupid little questions, but I'll never develop the deeper understanding of things that I want if I don't ask. Maybe it will also help other learners in the same boat as me.
I find the subject of earthing and bonding in bathrooms to be a source of confusion. I can't fully understand the actual situation with bathrooms and earth potential, and what the underlying principles are behind it.
I understand about it being a higher shock hazard due to the bare feet and wet conditions lowering bodily resistance, but don't have a good grasp of how this affects the earthing issue and some of the advice I have seen.
To illustrate, in the last few months I've come across quite a few installations where the wiring has been different.
For example, a bathroom with 4 230v light fittings where the supply went into a junction box and all the cables radiating out of this to the fittings had the cpc cut off at both ends so each cable had no cpc continuity. Is this correct? Wouldn't it have been better to have had cpc continuity down every cable going to the fittings, and just not terminate the cpc at the fitting, or is it normal and to regulation for these cables in the bathroom ceiling to not have cpc continuity down them?
I guess I'm asking is it correct to cut off the cpc at the bathroom entrance and have no cpc continuity going through any cable run in the ceiling to bathroom fittings, or should there be cpc continuity in these cables going around the bathroom ceiling even if there is to be no termination at the actual fitting?
Same when dealing with low voltage downlights. Every installation i've seen had a junction box at each fitting which fed a single transformer for each light. The cpc was not taken down to the light fitting on any installation, but on one installation I've seen the cpc cut off at both ends of all the cables so there's no earth continuity at all between the cables running from junction box to junction box in the ceiling. In other installations I've seen the cpc terminated at each junction box so the cables in the bathroom ceiling do have continuity. Which is the correct way, or is either acceptable?
I came across a bathroom the other week which had a 230v wall and ceiling light, both with exposed conductive parts which had earth continuity when tested. The ceiling light fitting had a single cpc conductor being run separately to a junction box in the loft as the light fitting wiring only had line and neutral conductors. Is this correct, or did the person who installed it do something wrong by introducing this earth continuity into the bathroom fittings?
I see it mentioned about not introducing earth potential into bathrooms, yet also see supplementary bonding being a necessity under certain conditions, which then introduces earth potential into these areas. I just don't fully understand the underlying principles behind these rules. If its better to keep earth potential out of bathrooms, why have this bonding?
If it's ok and safe to keep earth potential out of bathrooms, why allow earth potential into other areas of the house?
I'm obviously getting mixed up on this subject. I understand the general principle of equipotential bonding and earthing ensuring that exposed and extraneous conductive parts remain at the same potential so no current will flow if two different parts are touched. But if it is safer for that reason, why shouldn't exposed conductive parts in bathrooms be earthed, yet extraneous conductive parts should be? Won't they be at different potentials? Is it something to do with water spray and conductivity?
As you can see I am a little confused. No amount of reading or sources I find give me a satisfactory understanding. Can anyone help by answering these questions or pointing me to a good resource on the subject? I appreciate these may sound like stupid questions, but my lack of clarity on the matter has been bothering me for a while.
Last edited by a moderator: