Ze found to be too high, but maybe not?

[Des 56]

I would welcome any views and assistance on an installation in an hospital that I found today

I was asked to wire and fit sockets for a ring main to some dado trunking that had been erected by a builder

This was being wired from a single phase dist board which had a faulty 100m/amp rcd main switch

A couple of lights were added to an existing circuit

After wiring, tests were made and the Zdb was 4.54 ohms

This test was then taken at the main dist board with all earths still connected and simillar reading was obtained

Nobody with maintenance responsibility was at this small hospital,however I managed to talk to an estates manager that they contacted for me

I asked for access to where the incomer was located, but no help off anyone,

this was to look at what system earth was present

I would expect that it may be Tns,but am guessing

The estate manager was very indifferent to any problem,they have a maintenance crew and he would send their electricians to have a look as he put it,( because they are going to close it in a year and didn't want any money spent) and could I make the sockets live

If I were to fit rcbos instead of the 3871/1 mcbs in the board,does this comply with regs (given in a TT system the max Zs for a 30m/amp rcd is 1667 ohms) although the system is probably Tns and the Ze appears to be well above stated values for operation of these mcbs for a Tns

It was my intention originally to omit Rcd protection using the skilled instructed person bit.this changed my thinking

As a sort of postscript

When I replaced the main dist board cover after talking to this person,I looked at the Mcbs and noticed one tripple pole was off,I thought I had inadvertantly knocked this off and reset it,there was one almighty bang as I did so,I left it off ( this was nothing to do with the new install,but it makes me very concerned as to the state of this installation if a faulty circuit like that has been left connected

Your views would be welcome,thank you

 

[steptoe]

more information is needed here.

MUCH more

especially due to the conditions you are working in,

and the special aspects of working in a hospital, you do understand the differences from normal installations I hope.

 

[ianmacd]

I guess measuring Ze will be impossible as you will not be able to de-energise the site. Measure Zs at the head and if its TNS or TNCS and over their allowed maximums, get DNO out to fix.

 

[Des 56]

more information is needed here.MUCH more

especially due to the conditions you are working in,

and the special aspects of working in a hospital, you do understand the differences from normal installations I hope.

Yes, I am well aware of various installations and have many years experience and 2391 etc

If after giving a rough run down of the install I may rephrase the question

The installation area will be for admin with a few computers etc

The earthing and bonding of the main install hasn't been checked by me because I didn't think an issue would devlelop in this type of public building

The question, knowing that the mcbs will not disconnect in 0.4/5sec given those readings throughout, was for my installation,

As I understand In a Tn system

Fault protection would be covered by the rcd, but overcurrent would still require overcurrent device

The system as it stands relies mainly on overcurrent

My question is. does the inclusion of an rcd in a TN system make the maximum Zs 1667 ohms because that rcd is in circuit or does the max Zs for the 3871/1 30 amp remain at 1.53

I am not interested in the rest of the installation only whether my installation can be energised given these circumstances

Thanks for the reply this far

 

[steptoe]

Yes, I am well aware of various installations and have many years experience and 2391 etc If after giving a rough run down of the install I may rephrase the question

The installation area will be for admin with a few computers etc

The earthing and bonding of the main install hasn't been checked by me because I didn't think an issue would devlelop in this type of public building

The question, knowing that the mcbs will not disconnect in 0.4/5sec given those readings throughout, was for my installation,

As I understand In a Tn system

Fault protection would be covered by the rcd, but overcurrent would still require overcurrent device

The system as it stands relies mainly on overcurrent

My question is. does the inclusion of an rcd in a TN system make the maximum Zs 1667 ohms because that rcd is in circuit or does the max Zs for the 3871/1 30 amp remain at 1.53

I am not interested in the rest of the installation only whether my installation can be energised given these circumstances

Thanks for the reply this far

due to the nature of your reply, and considering your many years experience in this type of installation Im not sure if I would have the answers as to how to resolve your situation without having more site specific information.

 

[Des 56]

due to the nature of your reply, and considering your many years experience in this type of installation

I apologise if the reply gave an impression of being cocky or abrupt,it was not intended that way if that was the case or impression I gave

I asked this questions because of unusual circumstances for myself

I carry out installations that I know will comply normally, and was only looking to see if the regs can be looked at differently in this case, so that I could resolve the problem without having to escalate the argument with the people who are wanting power supplied and who carry out the mantenance

Thank you

 

[electrizion]

I would welcome any views and assistance on an installation in an hospital that I found todayI was asked to wire and fit sockets for a ring main to some dado trunking that had been erected by a builder

This was being wired from a single phase dist board which had a faulty 100m/amp rcd main switch

A couple of lights were added to an existing circuit

Replace faulty main switch

After wiring, tests were made and the Zdb was 4.54 ohms

This test was then taken at the main dist board with all earths still connected and simillar reading was obtained

Nobody with maintenance responsibility was at this small hospital,however I managed to talk to an estates manager that they contacted for me

I asked for access to where the incomer was located, but no help off anyone,

this was to look at what system earth was present

I would expect that it may be Tns,but am guessing

Assuming the sockets are a new cct you will need the origin details and I would insist on access and refuse to energise the cct until it was given

The estate manager was very indifferent to any problem,they have a maintenance crew and he would send their electricians to have a look as he put it,( because they are going to close it in a year and didn't want any money spent) and could I make the sockets live

If I were to fit rcbos instead of the 3871/1 mcbs in the board,does this comply with regs (given in a TT system the max Zs for a 30m/amp rcd is 1667 ohms) although the system is probably Tns and the Ze appears to be well above stated values for operation of these mcbs for a Tns

It was my intention originally to omit Rcd protection using the skilled instructed person bit.this changed my thinking

Again assuming there are other distribution boards within the property what are the Zdb readings of those?

As a sort of postscript

When I replaced the main dist board cover after talking to this person,I looked at the Mcbs and noticed one tripple pole was off,I thought I had inadvertantly knocked this off and reset it,there was one almighty bang as I did so,I left it off ( this was nothing to do with the new install,but it makes me very concerned as to the state of this installation if a faulty circuit like that has been left connected

I too would be concerned you would be wise to find out what this cct is and remove it from the db

dcw

 

[Des 56]

It is not my responsibility other than to inform them of their dangers that I am aware of,there is little concern on their part

 

[electrizion]

I believe that you do need to escalate this and refuse to make the ccts live until you have access to the source. If this access is refused for some reason or another remove your ccts from the db and inform them in writing of the problems

regards

dcw

 

[Des 56]

A assuming there are other distribution boards within the property what are the Zdb readings of those?

I did take a earth loop reading at the main distribution board and had same result.this was not at the origin of supply though

 

[Lee321]

same results in different locations! ?

are your testers ok?

 

[SteveH37]

If they have an in house maintenance team or a designated contractor then there should be records of inspection and testing which SHOULD be available to persons carrying out any works. Personally speaking, I would err on the side of caution and, as others have said, refuse to energise the circuit. This is an addition to an existing installation and as such requires a EIC which will require you to confirm supply characteristics, Ze (Zs probably as it's a hospital), main and supplementary bonding, phase rotation etc etc (not going to teach you to suck eggs).

My advice, cover yourself first and foremost, if the place goes up it'll be YOUR fault.

Just my opinion of course. put the kettle on

Steve.

 

[kme]

Errrrrr. Right!

I would expect that it may be Tns,but am guessing

So what would you have put on your cert. then mate?

You need either access to the incomer (unlikely) OR

Copies of the last PIAT / PIR carried out.

I wouldn`t be energising anything, without more info.

same results in different locations! ?are your testers ok?

The same thing occured to me.

This was being wired from a single phase dist board which had a faulty 100m/amp rcd main switch

1. Why does the SP board have a 100mA RCD front end?

2. Define "faulty"?

knowing that the mcbs will not disconnect in 0.4/5sec given those readings throughout, was for my installation

So which regs are you installing to??

KME

 

[batty]

I would think installation is TT. I cannot think of any other reason for having RCD as main switch in a hospital other than it being TT.

 

[Des 56]

Thanks for all the replies

Here is an update on the situation,with a few answers to some of the comments

Why does the SP board have a 100mA RCD front end?

Your guess is as good as mine.unknown,past issues maybe?

So what would you have put on your cert. then mate?

I would have put whatever the earth system turned out to be, after further investigation

You need access to the incomer

Agreed

or

Copies of the last PIAT / PIR carried out.

Estates manager said that past certificates were not available for inspection by me

same results in different locations! ?

are your testers ok?

Yes my testers are ok.they are used on a daily basis and checked and calibrated

The same result in a different location,was meant to convey that the readings were simillarly high (if it were Tns or Tnc-s)not that exact readings were found in different locations,although the dist boards were perhaps 15 meters only apart

I would think installation is TT. I cannot think of any other reason for having RCD as main switch in a hospital other than it being TT.

A reasonable assunption,not far off the mark

The main distribution board had no RCd protection (crabtree C 50 breakers only)so TT seemed unlikely given that set up

This was being wired from a single phase dist board which had a faulty 100m/amp rcd main switch

2. Define "faulty"?

The actual cover of the intergrated RCd fell off when the cover was taken off the board,test button and all

This was not RCd tested because of possible TT system and main front end RCd that may have taken the whole of that installation out

(knowing that the mcbs will not disconnect in 0.4/5sec given those readings throughout,)

So which regs are you installing to??

Dis connection of 0.4 for final circuits not exceeding 32 amp off the sub dist board and 5 sec for the sub main off the crabtree c50 for the distribution circuit

The installation was started only yesterday,so the 17th was in force then I guess (unless a new edition came out whilst I was at work)

An electricians mate went to the job this morning to arrange for me to have access Monday He was given access to the origin today

What he found was that the incomer is 3 phase and neutral overhead in singles,so likely TT

35 mm main earth to an old 3"Diameter water pipe, the cable core and the connection to the clamp was badly corroded

It is a shambles,that was his assessment, this is the main earth conductor for the installation at the origin

I have informed the estate manager over the phone that no energising of the new installation can take place until the issues are sorted out

His main concern was that word had gotten out to the staff that the installation was not as it should be and that finances dont allow for improvement

The man doesn't appear to regard a potentially dangerous electrical installation as anything more than a nuisance to him at this time because of the impending closure that he said was taking place next year

The contract via a builder has been completed in as far as I am concerned,with a non live circuit installed

I will also write a letter to the local area health authority voicing my concerns and to the HSE if appropriate

Finally,I wouldn't have believed that a public use building could be allowed to be in such a run down state, with perhaps years of neglect of the electrical installation

It has been an occasion to regret, considering that the job was in effect just a days work

Thanks again for the input

 

[steptoe]

Thanks for all the repliesHere is an update on the situation,with a few answers to some of the comments

Why does the SP board have a 100mA RCD front end?

Your guess is as good as mine.unknown,past issues maybe?

So what would you have put on your cert. then mate?

I would have put whatever the earth system turned out to be, after further investigation

You need access to the incomer

Agreed

or

Copies of the last PIAT / PIR carried out.

Estates manager said that past certificates were not available for inspection by me

same results in different locations! ?

are your testers ok?

Yes my testers are ok.they are used on a daily basis and checked and calibrated

The same result in a different location,was meant to convey that the readings were simillarly high (if it were Tns or Tnc-s)not that exact readings were found in different locations,although the dist boards were perhaps 15 meters only apart

I would think installation is TT. I cannot think of any other reason for having RCD as main switch in a hospital other than it being TT.

A reasonable assunption,not far off the mark

The main distribution board had no RCd protection (crabtree C 50 breakers only)so TT seemed unlikely given that set up

This was being wired from a single phase dist board which had a faulty 100m/amp rcd main switch

2. Define "faulty"?

The actual cover of the intergrated RCd fell off when the cover was taken off the board,test button and all

This was not RCd tested because of possible TT system and main front end RCd that may have taken the whole of that installation out

(knowing that the mcbs will not disconnect in 0.4/5sec given those readings throughout,)

So which regs are you installing to??

Dis connection of 0.4 for final circuits not exceeding 32 amp off the sub dist board and 5 sec for the sub main off the crabtree c50 for the distribution circuit

The installation was started only yesterday,so the 17th was in force then I guess (unless a new edition came out whilst I was at work)

An electricians mate went to the job this morning to arrange for me to have access Monday He was given access to the origin today

What he found was that the incomer is 3 phase and neutral overhead in singles,so likely TT

35 mm main earth to an old 3"Diameter water pipe, the cable core and the connection to the clamp was badly corroded

It is a shambles,that was his assessment, this is the main earth conductor for the installation at the origin

I have informed the estate manager over the phone that no energising of the new installation can take place until the issues are sorted out

His main concern was that word had gotten out to the staff that the installation was not as it should be and that finances dont allow for improvement

The man doesn't appear to regard a potentially dangerous electrical installation as anything more than a nuisance to him at this time because of the impending closure that he said was taking place next year

The contract via a builder has been completed in as far as I am concerned,with a non live circuit installed

I will also write a letter to the local area health authority voicing my concerns and to the HSE if appropriate

Finally,I wouldn't have believed that a public use building could be allowed to be in such a run down state, with perhaps years of neglect of the electrical installation

It has been an occasion to regret, considering that the job was in effect just a days work

Thanks again for the input

please dont take this the wrong way,

but,

are you an electrician?

because the term "main earth conductor" is a very DIY phrase,

there is NO SUCH THING.

 

[Des 56]

please dont take this the wrong way,but,

are you an electrician?

because the term "main earth conductor" is a very DIY phrase,

there is NO SUCH THING.

I would certainly take it the wrong way

The term used was to describe a single earth conductor of an installation,where no other existed and the system type was unknown

It could have been a protective bonding conductor or an earthing conductor

By the way

Read regulation 542.4.1

In every installation a Main earthing terminal shall be provided to connect the following to the earthing conductor

You contributed nothing other than being unhelpful and nit picking words from a long reply,

It could be reasonable to refer to a conductor that was connected to that main earth terminal as a main earth conductor in order to distinguish it from a protective bonding conductor,it is nothing more than a play with words and terminology was not the main concern,or should I say just concern and leave the main out in case you pick up on that

It would have been helpful perhaps if you had been able to contribute to the content rather than side issues such as terminology

If the content was a little off pace for yourself, maybe better contributing content where you are able

 

[kme]

Alright.

Before another 5-a-side ensues.

With regard to your comment about public buildings in "such a state" (paraphrased), They`re usually the worst offenders; because the "managers" are used to bullying everything through, the same way they`re trying to "bully" you.

if you speak to them again - you are entitled BY LAW to see the last inspection certificate, or PIR report. As the installation cannot be isolated to allow incomer tests, access to the previous test results are a must. If you can`t turn it off, how the hell are you going to cert. the main protective devices? Guesswork won`t do it.

"Assuming" the supply is TT? Because it`s overhead? I wouldn`t put that on a cert. mate.

So this RCD front end of this board cannot be de-energised? ohhhhhhhhhkayyyyyyyyyy. I`m scared now.

Don`t get me wrong, I`m not getting at you - but some more info is needed - by you, more than us, before you can proceed further with this.

AFAICS - you cannot issue a cert. for this work, as you are unable to perform the necessary tests; OR glean the info from another source, i.e. previous cert.

KME

 

[steptoe]

referring to the "earthing conductor" as the main earth is both misleading and wrong, and would IIRC constitute a fail of 2391,

it is plain and simply WRONG, as it implies that there is another means of earthing the installation.

it is not nit picking, but just simply one of those things that separates sparks, 5week wonders, and DIYers, not sure which cat you fall into, but to be mis using such basic terms makes me wonder.

1st year stuff that is.

 

[Lurch]

referring to the "earthing conductor" as the main earth is both misleading and wrong, and would IIRC constitute a fail of 2391,

And I thought I was a pedantic nit picker and general PITA.