Wet Locations

[pc1966]

I think it's that rainwater has a resistivity of 20k ohm cm. (figures vary!)

Interestingly it seems tap water is far more conductive at 1000-5000 ohm.m from here:

Understanding the Resistivity of Water - Sensorex Liquid Analysis Technology

Understanding the resistivity of water is important for a number of reasons. This article discusses this and how you are able to measure it!

sensorex.com

Down to 200 ohm.m for brackish river water. Not sure what a bath filed with soapy stuff would be!

 

[Cookie]

Interestingly it seems tap water is far more conductive at 1000-5000 ohm.m from here:

Understanding the Resistivity of Water - Sensorex Liquid Analysis Technology

Understanding the resistivity of water is important for a number of reasons. This article discusses this and how you are able to measure it!

sensorex.com

Down to 200 ohm.m for brackish river water. Not sure what a bath filed with soapy stuff would be!

In theory the voltage gradient would be worse in fresh water than salt water.

 

[Cookie]

Alright, so I came across this:

Supplementary bonding in bathrooms and shower rooms

Free essays, homework help, flashcards, research papers, book reports, term papers, history, science, politics

studylib.net

I am thinking that if disconnection time can be reduced to 0.17 seconds, the RCD is not needed from a safety sense. It would be nice is BS7671 took this into consideration.

Just thinking out loud.

 

[pc1966]

I am thinking that if disconnection time can be reduced to 0.17 seconds, the RCD is not needed from a safety sense. It would be nice is BS7671 took this into consideration.

No, the RCD is still needed in my view unless you have eliminated single-fault risks.

So if you have supplementary bonding then you have to have two "unobserved" faults before a short L-E becomes dangerous, both the original CPC and the supplementary bonding, to expose a person to a dangerous voltage. Up to the 16th (I think) that was the norm for wet areas in the UK.

If you only had the CPC and very fast OCPD then an open CPC fault leaves the person completely unprotected against a L-E fault.

Now that RCDs are cheap and readily available they should be used for all sorts of reasons. I still don't like depending on them as my primary means of disconnection due to the single "unobserved" fault risk (and higher probability of that than MCB sticking or fuse somehow failing to blow), but on any new systems they make sense as additional protection.

 

[Cookie]

No, the RCD is still needed in my view unless you have eliminated single-fault risks.

So if you have supplementary bonding then you have to have two "unobserved" faults before a short L-E becomes dangerous, both the original CPC and the supplementary bonding, to expose a person to a dangerous voltage. Up to the 16th (I think) that was the norm for wet areas in the UK.

If you only had the CPC and very fast OCPD then an open CPC fault leaves the person completely unprotected against a L-E fault.

Now that RCDs are cheap and readily available they should be used for all sorts of reasons. I still don't like depending on them as my primary means of disconnection due to the single "unobserved" fault risk (and higher probability of that than MCB sticking or fuse somehow failing to blow), but on any new systems they make sense as additional protection.

Correct, but as you say I do not like an RCD being the primary means to protect a user. In my opinion they supplemental or backup protection.

 

[LastManOnline]

Correct, but as you say I do not like an RCD being the primary means to protect a user. In my opinion they supplemental or backup protection.

Agreed. An rcd as a primary means of protection never sat right. It's best suited to a "support role", basically plugging the holes that primary protection can't provide. It plays a supplementary but vital role.

 

[Cookie]

Agreed. An rcd as a primary means of protection never sat right. It's best suited to a "support role", basically plugging the holes that primary protection can't provide. It plays a supplementary but vital role.

Agreed.