IET logo
 
IET
Decrease font size
Increase font size
Topic Title: N-E Link
Topic Summary:
Created On: 20 January 2014 04:26 PM
Status: Post and Reply
Linear : Threading : Single : Branch
1 2 Next Last unread
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 20 January 2014 04:26 PM
User is offline View Users Profile Print this message



rondo

Posts: 26
Joined: 22 June 2004

We have a main switchboard with a N-E link on the standby generator (450kVA) incoming supply.

The generator has been supplied with an internal N-E Link within the connection box. Apparently this is the normal arrangement.

Should I have the N-E link removed on the main switchboard or can I run with both in place?

Rondo
 20 January 2014 04:56 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 1056
Joined: 04 November 2004

What type of earthing system do you have on the normal supply?

Regards
 20 January 2014 08:15 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19837
Joined: 23 March 2004

Can you run mains and generator as synchonised - removing the link at the switch board may well act on the mains supply - and you certainly don't want to see that floating.

Do you have 3 or 4 pole devices on the mains and generator main switches

If you have a N-E link at the switchboard, then usually there will be one each at the incoming side of the mains and generator devices or you have one internal to the board (ie permanently connected) - in either case, you would then not have one at the generator set.

Needas a bit more of a description to answer further

Regards

OMS

-------------------------
Failure is always an option
 21 January 2014 05:44 PM
User is offline View Users Profile Print this message



rondo

Posts: 26
Joined: 22 June 2004

OMS Thanks for the response,

The arrangement is as follows:

1. Essential Switchboard Incoming breaker is a 800A 4P ACB with the N-E link located on the incoming side of the mains.

2. Supply from the Generator outgoing to the essential switchboard is a 800A 3P MCCB with the N-E link between the set and the outgoing breaker.

3. The set up at present does not allow for the mains and Gen set to run as synchronised.

Rondo
 21 January 2014 06:22 PM
User is offline View Users Profile Print this message



jcm256

Posts: 1921
Joined: 01 April 2006

Rondo

Oms will sort you out, but out of interest,
(1) Do you have a 3-pole or 4-pole change over switch between the main switchboard and the essential switchboard. (to connect the generator / isolate the mains)

(2) or is it a special key arrangement.
(3) When you say neutral earth link is at the incoming side of the mains, do you mean the supply transformer located in a compound for your supply only, or like normal TN-C-S a link between N-E at the mains supply service head.

Generator sets don't always come with that N-E link installed. The manufacture leaves it up to the installer to sort out the earthing arrangements.
 21 January 2014 07:28 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19837
Joined: 23 March 2004

Originally posted by: rondo

OMS Thanks for the response,

The arrangement is as follows:

1. Essential Switchboard Incoming breaker is a 800A 4P ACB with the N-E link located on the incoming side of the mains.

OK, so when the mains drops out, the ACB opens and you retain the N-E link in place


2. Supply from the Generator outgoing to the essential switchboard is a 800A 3P MCCB with the N-E link between the set and the outgoing breaker.

OK - so with the mains ACB open, you still have the N-E link to reference the installation and as you have a 3 pole ACB, so you don't need anther link -

3. The set up at present does not allow for the mains and Gen set to run as synchronised.

OK - so open transition with only the mains or the generator breaker closed at any one time, the N-E link is always present, you have 4 pole mains and 3 pole generator breakers so your existing N-E link is fine - you don't need one at the gen set - if you leave it in place it is effectively a N-E fault within the installation


Rondo


Regards

OMS

-------------------------
Failure is always an option
 22 January 2014 06:40 AM
User is offline View Users Profile Print this message



MickeyB

Posts: 181
Joined: 18 January 2003

I think the OP noted the NE was on the unswitched side of the ACB....... maintaining an effective NE for the transformer.
Typical to have NE on the unswitched side of 4 pole ACB.

Use of TPN for the gen is a problem..... NE contactor or MCCB would be best way to control and maintain single NE if required during transition. 2 NE reference is utility mode could be a problem......
 22 January 2014 08:50 AM
User is offline View Users Profile Print this message



rondo

Posts: 26
Joined: 22 June 2004

To All,

Many thanks for your responses on this matter.

Kind Regards
Rondo
 22 January 2014 10:13 AM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19837
Joined: 23 March 2004

Originally posted by: MickeyB

I think the OP noted the NE was on the unswitched side of the ACB....... maintaining an effective NE for the transformer.

Typical to have NE on the unswitched side of 4 pole ACB.

Use of TPN for the gen is a problem..... NE contactor or MCCB would be best way to control and maintain single NE if required during transition. 2 NE reference is utility mode could be a problem......


I'm not sure I follow why a 3 pole rather than 4 pole ACB on the generator is a problem, Mickey.

We noted the N-E bond remains present regardless of the mains ACB status, that is 4 pole to prevent neutral "export".

There is only one generator so we won't see circulating neutral currents.

Ditto as the mains and gen set do not parallel operate

I'm sure you have a reason, but I'm struggling to see why the gen set neutral needs isolation when mains is present- given that it is solidly earthed.

I'm assuming here that the mains supply is actually direct from a client or DNO transformer btw - effectively PNB (or TN-S to be controversial)

Regards

OMS

-------------------------
Failure is always an option
 22 January 2014 11:40 AM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 1056
Joined: 04 November 2004

Standby (island) operation

The star point should be permanently connected to the main earthing terminal for both supply systems. However it should be noted that a neutral switch is required for a non-PME supply, see Figure 10.15. It is important to note that where the LV supply is derived from a consumer's substation the neutral switch is not needed.


Regards
 22 January 2014 11:45 AM
User is offline View Users Profile Print this message



MickeyB

Posts: 181
Joined: 18 January 2003

4 pole ACB will mean the neutral is isolated when ACB opens.
NE link before ACB to ensure TX neutral is connected to earth at all times.

If TPN on gen then 2No. NE points in use in utility mode with gen ACB open.
 22 January 2014 01:11 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19837
Joined: 23 March 2004

Originally posted by: MickeyB

4 pole ACB will mean the neutral is isolated when ACB opens.

Yes agreed

NE link before ACB to ensure TX neutral is connected to earth at all times.

Again agreed


If TPN on gen then 2No. NE points in use in utility mode with gen ACB open.

But only if there is also a N-E bond at the alternator - I think I was suggesting that it relied on the N-E bond at the mains ACB and that the switchboard earth bar also had connection to the generator (or probably site LV electrode)




It is important to note that where the LV supply is derived from a consumer's substation the neutral switch is not needed.


LoL - have you been reading CIBSE Guide K, Parsley

If it's connected to a client ransformer and has the N-E link at the switchboard, then it's basically PNB. So for this purpose, you could read the requirment from the Guide K diagram for PME and island operation - ie the one with the 3 pole Generator protection


Regards both

OMS

-------------------------
Failure is always an option
 22 January 2014 01:28 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 1056
Joined: 04 November 2004

OMS, I knew you would recognise that text.

Wouldn't it be the TN-S drawing 10.15a) but without the neutral switch at the Genie, if connected in island and PNB?

i.e.3 pole at genie and 4 pole at the main switchboard I think that's what the OP describes.

Also I think there's a mistake on drawing 10.14b)

Regards
 22 January 2014 01:53 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19837
Joined: 23 March 2004

LoL -

Isn't is as 10.15 b if you are using Guide K

Regards

OMS

-------------------------
Failure is always an option
 22 January 2014 02:13 PM
User is offline View Users Profile Print this message



MickeyB

Posts: 181
Joined: 18 January 2003

I'm a little confused........

How many NE points do we have in service when in utility or generator mode?
1 NE with Utility 4 pole ACB closed via NE link in front of the ACB.
1 NE link in the switchboard to maintain the NE link when you switch the Utility ACB OFF/ break the 4th pole?
1 NE link via the TP&N ACB at the generator?

I thought BS 7410.... or maybe another standard..... advised to have TP&N or 4P throughout (when deriving a separate neutral) and don't mix the 2 unless you want to use a NE contactor..... NE via the switchboard with TP&N keeps it simple..... single point of earthing......

If you mix 4P & TP&N then you could have 2 points of NE reference at any one time?
 22 January 2014 03:31 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 1056
Joined: 04 November 2004

Originally posted by: OMS

LoL -



Isn't is as 10.15 b if you are using Guide K



Regards



OMS


OMS

10.15b) is PME and shows a 3P switch at the switch board and at the genie the OP states Essential Switchboard Incoming breaker is a 800A 4P ACB with the N-E link located on the incoming side of the mains. I thought the set up sounded like PNB (TNS) that's why I asked the question about the earthing system in my first post.

The reference to 10.14b) has nothing to do with this post but as you know the guide I thought you might take a look.

Regards
 22 January 2014 03:45 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19837
Joined: 23 March 2004

10.15 (b) has a 4 pole mains and 3 pole generator breaker doesn't it ?

It's labelled as PME, but noting this is a private supply and PNB, it is what the OP is describing.(lets not ignite the PNB - is it TN-S or TNC-S just yet)

10.14(b) is clearly wrong as no Neutral - Earth link.

In 10.14(b), it doesn't need a 4 pole mains ACB as it's parallel operation - if you wanted close transition so it reverted to island mode on LoM then it would need a 4 pole and specific G59 protection modifications. Failing that, it would need to open up and drop out the generator on LoM (typical of CHP plant)

Regards

OMS

-------------------------
Failure is always an option
 22 January 2014 04:01 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 1056
Joined: 04 November 2004

10.15 (b) has a 4 pole mains and 3 pole generator breaker doesn't it ?
Ooppss yes it does actually show 4P at the mains but the N at the mains doesn't appear to be interlinked with the genie's switch is that another mistake?

10.14(b) is clearly wrong as no Neutral - Earth link.
yep

Regards
 22 January 2014 05:18 PM
User is offline View Users Profile Print this message


Avatar for OMS.
OMS

Posts: 19837
Joined: 23 March 2004

Yes, the little dotted line denoting the interlocking should extend to the neutral pole of the Mains changeover device.

That's what you get when you give the clankies down at Balham the chance to play around with systems they don't really understand - it's all a bit modern, the electrickery stuff, to our mechanical brethren - after all we've only been at it about 120 years - the clankies have been making fire since the stone age

Regards

OMS

-------------------------
Failure is always an option
 22 January 2014 05:29 PM
User is offline View Users Profile Print this message


Avatar for Parsley.
Parsley

Posts: 1056
Joined: 04 November 2004

Originally posted by: OMS

Yes, the little dotted line denoting the interlocking should extend to the neutral pole of the Mains changeover device.



That's what you get when you give the clankies down at Balham the chance to play around with systems they don't really understand - it's all a bit modern, the electrickery stuff, to our mechanical brethren - after all we've only been at it about 120 years - the clankies have been making fire since the stone age



Regards



OMS


I always thought it was the institution of choice for consultants OMS.

Regards
IET » Wiring and the regulations » N-E Link

1 2 Next Last unread
Topic Tools Topic Tools
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.