Ze test with RCD main switch

[kuffs]

Hi everyone, I am new to the forum and to the world of electrical installations. I completed my domestic electrical training back in August and so far have not gone for scheme membership as I am a stickler for making sure I get things right before committing to working on a customers installation. Sorry, am rambling. I'll get to the point.

I am doing various tests on my own installation and I got a slightly high Ze measurement (.39) TNCS. At the time I took the measurenent at the main switch in the CU. Although the current at this measurement would be enough to clear the service fuse (60A BS1361) in .4 seconds, I was left wondering if I should have measured at the RCD main switch which is on the meter tails before the CU? I have just done the test at that point and got 0.17 ohms, which is a vast improvement, I also retested at the CU main switch and got 0.34 ohms which is also better than the other day. The overall point is, where is the correct position to take the reading?

I look forward to your comments. Thank you.

 

[a1]

Did you Isolate the supply and disconnect the main earthing conductor for your Ze test?

 

[SPECIAL LOCATION]

Hello Kuffs.......

"I completed my domestic electrical training back in August"

Short course?

fleecing training company?

Did this course not go through using the regs or on site guide?

When I did my C&G's a college when I were younger...

We had to go through this sort of stuff both practical & theory..

twas part of the learning :|

To answer your question you will need to read:-

On-site-guide 10.3.6. Earth fault loop impedance..

The bit about effectiveness of the distributor

 

[kuffs]

Hi Guys, Yes it was a training company and I think I know how you fellas feel about them and people like me who go on them. However, as I mentioned in my original post I am very very consiensious. I also have a background in a similar area, as I did my apprenticeship as an auto electrician a very long time ago and worked for 10 years in that trade. I appriciate that this does not make me a domestic electrician and neither does the 17 day course i went on.

To get back to my issue I, Definately isolated and removed the main earth from MET. Metered at the earth cable (now removed) and the line on the incoming side of the main switch. My reason for this post was that I had already concluded that the RCD main switch could be creating a resistance and effecting the readings, hence my re-taking the reading at that point to confirm my suspicions.

I am also aware of 10.3.6 as this is how I'm conducting the test, this section only says that the main switch is opened and made secure. This does not really answer the question as to which switch, in my case, is considered the main switch. Is it the RCD main switch or the CU main switch?

I have taken a look at P87 as suggested but this is the contents page for Part 5 in the red book. As for the minimizing inconvenience, I am aware of this also but the RCD was already installed when I moved in to the property, so I don't know why it was installed, unless it was done when the electric shower was fitted. In any case it is my intention to replace the CU with a split load unit in the near future, as one of my jobs for inspection to become a scheme member.

Please don't think any of my comments above are sarcastic, because they are not. I know how these things can read sometimes. Your help is greatly appreciated. Thank you.

 

[Zeespark]

If its a TNCS system and you have the cash why not do a Main Switch/RCBO installation?

AndyGuinness

 

[Theorysparky]

split load or dual board ???

 

[SPECIAL LOCATION]

Hi Guys, Yes it was a training company and I think I know how you fellas feel about them and people like me who go on them. However, as I mentioned in my original post I am very very consiensious. I also have a background in a similar area, as I did my apprenticeship as an auto electrician a very long time ago and worked for 10 years in that trade. I appriciate that this does not make me a domestic electrician and neither does the 17 day course i went on.

"I am very very conscientious. I also have a background in a similar area...."

Sorry but auto electrician is not quite going to cover all the basics for AC distribution in homes and offices...

What qualifications did you earn whilst doing your auto electrics?

Even with a 17 day... (3 & bit weeks) course... This in my mind is not the evidence of someone who is very conscientious...

To put my views into context I was originally trained as a Telecommunications engineer doing a 4 year Apprenticeship many moons ago...

Gaining HNC in telecoms engineering along the way..

Following redundancy approx 15 years ago I changed trades and went off doing approx 3 years worth of night classes at college...

whilst starting my own electrical business...

Gaining C&G 2360, C&G 2381, C&G 2391, C&G 2382 ..

Covering the practical installation work and electrical theory and inspection and testing and understanding of the regs Inc updates to 17th...

Now from my own personal knowledge I would have to say it is dam near impossible to cover all the ESSENTIAL basics in a 17 days course...

I do know what it is like to change career and start up your own business whilst supporting a wife & family..

There are NO easy short cuts....

I am sorry to say this but personally it sounds to me like you have been ripped off...

To get back to my issue I, Definately isolated and removed the main earth from MET. Metered at the earth cable (now removed) and the line on the incoming side of the main switch. My reason for this post was that I had already concluded that the RCD main switch could be creating a resistance and effecting the readings, hence my re-taking the reading at that point to confirm my suspicions.

I am also aware of 10.3.6 as this is how I'm conducting the test, this section only says that the main switch is opened and made secure. This does not really answer the question as to which switch, in my case, is considered the main switch. Is it the RCD main switch or the CU main switch?

I have taken a look at P87 as suggested but this is the contents page for Part 5 in the red book. As for the minimizing inconvenience, I am aware of this also but the RCD was already installed when I moved in to the property, so I don't know why it was installed, unless it was done when the electric shower was fitted. In any case it is my intention to replace the CU with a split load unit in the near future, as one of my jobs for inspection to become a scheme member.

Please don't think any of my comments above are sarcastic, because they are not. I know how these things can read sometimes. Your help is greatly appreciated. Thank you.

If you have come away from a "Domestic installer

 

[kuffs]

I'm don't really know how much more clear I can be here. I have already said that I have a background in a similar trade. I also said that I know that that trade does not make me a domestic electrician, nor does the 17 day course I did. I am though, trying to point out that I am doing my damnedest to make sure that my knowledge is as good as it can be. I agree that these short courses are insufficient to impart the knowledge required, but you tell me what you would do if you had just invested over

 

[SPECIAL LOCATION]

I'm don't really know how much more clear I can be here.

And I don

 

[Ash]

Ze is the impedance external, so I guess in your case take the reading from the RCD as that's the first point from the meter itself.

As others have pointed out, why is the RCD there in the firstplace?

If it's your own home why not sort it all out, 10-way units fully loaded, Dual RCD can be found for

 

[stuartrw79]

"I am very very conscientious. I also have a background in a similar area...."Sorry but auto electrician is not quite going to cover all the basics for AC distribution in homes and offices...

What qualifications did you earn whilst doing your auto electrics?

Even with a 17 day... (3 & bit weeks) course... This in my mind is not the evidence of someone who is very conscientious...

To put my views into context I was originally trained as a Telecommunications engineer doing a 4 year Apprenticeship many moons ago...

Gaining HNC in telecoms engineering along the way..

Following redundancy approx 15 years ago I changed trades and went off doing approx 3 years worth of night classes at college...

whilst starting my own electrical business...

Gaining C&G 2360, C&G 2381, C&G 2391, C&G 2382 ..

Covering the practical installation work and electrical theory and inspection and testing and understanding of the regs Inc updates to 17th...

Now from my own personal knowledge I would have to say it is dam near impossible to cover all the ESSENTIAL basics in a 17 days course...

I do know what it is like to change career and start up your own business whilst supporting a wife & family..

There are NO easy short cuts....

I am sorry to say this but personally it sounds to me like you have been ripped off...

If you have come away from a "Domestic installer

 

[steptoe]

make sure you are on the correct main earth cable

---------- Post Auto-Merged at 18:10 ---------- Previous post was made at 18:08 ----------

I cannot understand the mentality of some on this forum, why can`t you just answer the OP `s question, without questioning there credentials. I have read many times on here that this forum was set up with the intention of helping students and learners alike. I am surprised anybody asks anything when this is the responses they get!!Before belittling what courses the OP has or hasn`t done I would take a look at your own training, You state you completed the C&G 2360 ( nights 2.5hrs a week for about 39 weeks ? ) over three years work out how many days that is before you laugh to much at 17 days. Think the 2360 was intended to be partaken as part of a 4/5 year apprenticeship, including 2391, 2382 and the most important ant AM2 trade test, whilst working as an apprentice for the other 4 days a week under the supervision of a qualified Electrician!!

The OP is only trying to learn on his own installation unlike yourself who having completed your night school thought you where competent to carry out work on your own as a business!!

I too did the 2360 Part 1 and part 2, 2391,2382, and AM2 in conjunction with a 4 year apprentice, with a company who did large range of electrical work from domestic to agricultural and I for one would never have thought myself competent having sat the C&G courses alone!!

whoa, slow down there,

I think the frustration bears out from having pointed out to the OP where he will find the answers the same question is being asked again.

 

[kme]

I cannot understand the mentality of some on this forum, why can`t you just answer the OP `s question, without questioning there credentials.

I think you`ll find that many of us DO answer the question, by advising on where to look to find the answer, rather than saying "you must do such-and-such." How constructive would that be?

I have read many times on here that this forum was set up with the intention of helping students and learners alike. I am surprised anybody asks anything when this is the responses they get!!

To be honest; I find the lack of knowledge in many posts far more surprising (and I am not referring to the O/P, or anyone in particular). If a student asks a question; I would prefer to point them in the direction of the answer, and get them to think for themselves, to be honest. Those who get upset with that are the ones who took a 5WFW course, KNOWING it wasn`t the "real deal", but too lazy to learn the trade properly.

Before belittling what courses the OP has or hasn`t done I would take a look at your own training, You state you completed the C&G 2360 ( nights 2.5hrs a week for about 39 weeks ? ) over three years work out how many days that is before you laugh to much at 17 days. Think the 2360 was intended to be partaken as part of a 4/5 year apprenticeship, including 2391, 2382 and the most important ant AM2 trade test, whilst working as an apprentice for the other 4 days a week under the supervision of a qualified Electrician!!

I assumed (always a bad idea) that Special Location was using his background as a reference for the O/P, that he too had changed track; but took the C&G route to gain the qualifications. Maybe I`m wrong?

The OP is only trying to learn on his own installation unlike yourself who having completed your night school thought you where competent to carry out work on your own as a business!!

Having read the posts in this thread alone, I know which member I would want to work on my property mate..........

I too did the 2360 Part 1 and part 2, 2391,2382, and AM2 in conjunction with a 4 year apprentice, with a company who did large range of electrical work from domestic to agricultural and I for one would never have thought myself competent having sat the C&G courses alone!!

I don`t believe this thread needs to devolve into "my list of quals & experience is longer than yours" type of affair - As stated above, SL was, IMO, pointing out the differences in levels of training & qualification. I too would have aimed the O/P in the direction he should be looking, not simply said "Oh, you need to test it at this point - the O/P learns nothing of value from such a post, other than my opinion. Pull your horns in a bit matey - Spec`s posts have earned him one of the highest reputations on the forum for a reason.............

KME

 

[stuartrw79]

I think you`ll find that many of us DO answer the question, by advising on where to look to find the answer, rather than saying "you must do such-and-such." How constructive would that be?To be honest; I find the lack of knowledge in many posts far more surprising (and I am not referring to the O/P, or anyone in particular). If a student asks a question; I would prefer to point them in the direction of the answer, and get them to think for themselves, to be honest. Those who get upset with that are the ones who took a 5WFW course, KNOWING it wasn`t the "real deal", but too lazy to learn the trade properly.

I assumed (always a bad idea) that Special Location was using his background as a reference for the O/P, that he too had changed track; but took the C&G route to gain the qualifications. Maybe I`m wrong?

Having read the posts in this thread alone, I know which member I would want to work on my property mate..........

I don`t believe this thread needs to devolve into "my list of quals & experience is longer than yours" type of affair - As stated above, SL was, IMO, pointing out the differences in levels of training & qualification. I too would have aimed the O/P in the direction he should be looking, not simply said "Oh, you need to test it at this point - the O/P learns nothing of value from such a post, other than my opinion. Pull your horns in a bit matey - Spec`s posts have earned him one of the highest reputations on the forum for a reason.............

KME

Thanks for that KME, but I think we are all entitled to our own opinion, I am sure Special Location can stand up for himself and doesn

 

[kme]

Then I shall :coat

 

[kuffs]

Unfortunately, it seems that this has all got out of hand based in part on my misunderstanding of what special location's precise intentions were and some assumptions made about my abilities. I came to this forum with what I thought was a question I would get a simple answer to. Sadly, through the misunderstandings and assumptions made, this as become very difficult. Part of the problem is that I do understand the implications of all that Special Location has pointed out, but he doesn't know me from Adam and cannot therefor know my abilities.

I am very comfortable with the fact that I am getting 0.34 ohms at the CU main switch and what this means in terms of Zs etc. When I did the test, the first place I went was the CU main switch as this is what I was taught. When I got a reading above 0.35 ohms I wanted to know why. After thinking it over I went back to it a few days later with the thought that maybe the RCD main switch was effecting the reading. When I measured Ze at the RCD I got 0.17 ohms which is obviously a big difference. From this, I deduced that if the RCD main switch was removed from the circuit I would get 0.17 ohms at the CU main switch. This would then mean my fuses would clear a fault much quicker. I hope that all members can see that all I am trying to do is make accurate and correct judgments in order to work safely and effectively.

 

[steptoe]

kuffs,

I havent answered your question for a couple of reasons,

1 Im getting very confused by your reference to various main switches, I honestly am confused by where each switch is and what its purpose is,

you only have one main switch for each consumer unit,

2 on a similar token, main earthing conductor ?

Im confused by this too, do you mean the 'earthing conductor' ?, ie, the earth from the cut-out

 

[kuffs]

Hi Steptoe, Sorry for the confusion. I have a TNCS system with an RCD on the meter tails prior to the CU and you are right it is the earthing conductor from the cut-out. I must stop calling it a main earthing conductor.

 

[SPECIAL LOCATION]

I cannot understand the mentality of some on this forum, why can`t you just answer the OP `s question, without questioning there credentials. I have read many times on here that this forum was set up with the intention of helping students and learners alike. I am surprised anybody asks anything when this is the responses they get!!Before belittling what courses the OP has or hasn`t done I would take a look at your own training, You state you completed the C&G 2360 ( nights 2.5hrs a week for about 39 weeks ? ) over three years work out how many days that is before you laugh to much at 17 days. Think the 2360 was intended to be partaken as part of a 4/5 year apprenticeship, including 2391, 2382 and the most important ant AM2 trade test, whilst working as an apprentice for the other 4 days a week under the supervision of a qualified Electrician!!

The OP is only trying to learn on his own installation unlike yourself who having completed your night school thought you where competent to carry out work on your own as a business!!

I too did the 2360 Part 1 and part 2, 2391,2382, and AM2 in conjunction with a 4 year apprentice, with a company who did large range of electrical work from domestic to agricultural and I for one would never have thought myself competent having sat the C&G courses alone!!

I presume this is written to yourself?

As you have not answered the OPs question.. (which I have 3x in all my previous posts)

AND

you are questioning other members credentials and/or the way they answer the various posts?

It could be said that Pot Kettle & Black fit together somehow ???

:|

---------- Post Auto-Merged at 21:20 ---------- Previous post was made at 20:49 ----------

Unfortunately, it seems that this has all got out of hand based in part on my misunderstanding of what special location's precise intentions were and some assumptions made about my abilities. I came to this forum with what I thought was a question I would get a simple answer to. Sadly, through the misunderstandings and assumptions made, this as become very difficult. Part of the problem is that I do understand the implications of all that Special Location has pointed out, but he doesn't know me from Adam and cannot therefor know my abilities.I am very comfortable with the fact that I am getting 0.34 ohms at the CU main switch and what this means in terms of Zs etc. When I did the test, the first place I went was the CU main switch as this is what I was taught. When I got a reading above 0.35 ohms I wanted to know why. After thinking it over I went back to it a few days later with the thought that maybe the RCD main switch was effecting the reading. When I measured Ze at the RCD I got 0.17 ohms which is obviously a big difference. From this, I deduced that if the RCD main switch was removed from the circuit I would get 0.17 ohms at the CU main switch. This would then mean my fuses would clear a fault much quicker. I hope that all members can see that all I am trying to do is make accurate and correct judgments in order to work safely and effectively.

Hello again Kuffs...

First off your original question was

The overall point is, where is the correct position to take the reading?

Which I have answered 3 times already...yet ignored by some :|

as some people seem to be missing the words in my earlier posts...

As you now elaborate a bit more about your level of understanding I do also hope you can understand why any person electrically trained would find your initial question rather basic to say the least..

I was trying to get you to think about the WHY something is or is not acceptable rather than the WHAT we do...

Being spoon fed do 'A' then 'B' then 'C' and you will get 'D'

Is no use to any person who may be working alone on an electrical installation they are going to leave energised for someone else to use..

We have to understand

 

[kuffs]

Hi Special Location, Please accept my apologies for misunderstanding your approach to my problem. I do fully agree that the way you were trying to get me to think about the problem, was indeed the best approach. I think the problem stemed from the fact that I am already reasonably comfortable with the parts of the book you were pointing me towards and I could not understand why you kept pushing me back towards them. I do really appreciate your efforts. Sorry for misunderstanding.