Hi,
I've come across a non M.E.N distribution board that feeds a seperate M.E.N SwitchBoard.
ie. Main M.E.N Switch Board closest to the PoS ---> non M.E.N Distribution Board ---> OutBuilding M.E.N SwitchBoard
Is there anything that prohibits this configuration?
At the moment the PEN conductor that runs to the M.E.N distribution Board is in its own neutral terminal at the non M.E.N Distribution Board supplying the M.E.N Board
So far I can only find 5.5.3.1(b)(v), but I feel that would only apply if they were all PEN conductors??
If I crimped the PEN conductor to the SubMain neutral as per 5.5.3.1(b)(v), does that then turn that SubMain Neutral into a PEN conductor? So then would I also need to crimp the SubMain Neutral (now a PEC conductor?) to the PEN Neutral at which it is supplied from ie. Main SwitchBoard closest to the PoS?
Thanks
PEC Submain from Non M.E.N switchBoard
Re: PEC Submain from Non M.E.N switchBoard
Short answer: this config is non-compliant
If installing PEN submain i.a.w. 5.5.3.1 (b),
item (iv) says the submain can come either(A) from MSB, or (B) via intermediate DB(s) .
If using (B), then (v) kicks in, and integrity of the PEN must not depend on any connections to terminals in the intermediate swbd(s).
Ie you can pass through the intermediate swbd, and tap off to its N&E bar, but you can't terminate incoming & outgoing to any termonal of the intermediate swnd.
Effectively this prohibits what you are suggesting, as in this case the submain to DB1 has separate N & E conductors, terminated to respective bars of DB1, and then there's an outgoing PEN from DB1 to DB 2.
If installing PEN submain i.a.w. 5.5.3.1 (b),
item (iv) says the submain can come either(A) from MSB, or (B) via intermediate DB(s) .
If using (B), then (v) kicks in, and integrity of the PEN must not depend on any connections to terminals in the intermediate swbd(s).
Ie you can pass through the intermediate swbd, and tap off to its N&E bar, but you can't terminate incoming & outgoing to any termonal of the intermediate swnd.
Effectively this prohibits what you are suggesting, as in this case the submain to DB1 has separate N & E conductors, terminated to respective bars of DB1, and then there's an outgoing PEN from DB1 to DB 2.
Re: PEC Submain from Non M.E.N switchBoard
(v), says "... via distribution boards in one or more other outbuildings," and goes on to describe the continuity of the PEN conductor.AlecK wrote: ↑Fri Nov 29, 2024 3:18 pmShort answer: this config is non-compliant
If installing PEN submain i.a.w. 5.5.3.1 (b),
item (iv) says the submain can come either(A) from MSB, or (B) via intermediate DB(s) .
If using (B), then (v) kicks in, and integrity of the PEN must not depend on any connections to terminals in the intermediate swbd(s).
Ie you can pass through the intermediate swbd, and tap off to its N&E bar, but you can't terminate incoming & outgoing to any termonal of the intermediate swnd.
Effectively this prohibits what you are suggesting, as in this case the submain to DB1 has separate N & E conductors, terminated to respective bars of DB1, and then there's an outgoing PEN from DB1 to DB 2.
To me, that is saying that the intermediate DB is supplied by a PEN submain, and that is where the outgoing PEN submain neutral should be permanently connected to the incoming PEN neutral so it isn't relying on the "terminals on such distribution boards" for continuity.
The situation that Slovett is describing the intermediate DB is a "non MEN DB", so on a PEC submain, and the outgoing PEN neutral can be connected to the neutral bar as normal.
Re: PEC Submain from Non M.E.N switchBoard
Item (v) arises only if taking option (B) of item (iv).
Option B is that supply to the outbuilding DB is via one or more other DB that are in other outbuildings, and not direct from MSB.
Noting that there is no valid option of supply via DBs in main building, only via DBs in other outbuildings.
Keeping it simple; we have new OB 2 supplied by Submain 2 which is fed from DB1 in OB1, which is fed from MSB.
(v) applies to the PEN conductor of (new) submain 2 to OB2.
It requires that continuity of the PEN must not rely on any terminals of DB1.
So correct that, at DB1, if the incoming submain 1 supplying DB1 has a PEN; then the outgoing PEN of submain 2 cannot be connected to N-bar of DB1, but instead must be connected directly to incoming N of submain 1; with a tee-off to the N-bar of DB1
In Slovett's case, the incoming submain 1 to DB1 is not PEN, but instead has separate N + PEC.
Item (v) says nothing about whether (intermediate) DB1 is fed with a PEN or by a N + separate PEC, so same rule applies.
So in this case also the outgoing PEN of submain 2 cannot be connected to N-bar of DB1, but instead must be connected directly to incoming N of submain 1.
A PEN conductor serves 2 separate and distinct functions.
as an N conductor, it has to carry return / out-of-balance load current.
As a PE conductor, it has to carry earth fault currents and also equipotential bonding.
It's this PE function that can't be compromised by being disconnected at DB1.
All points required to be earthed must have continuity at all times back to main earthing terminal at MSB.
If the outgoing PEN of submain 2 is connected to N-bar of DB1, then disconnection of either that connection , or of the incoming N of submain 1, would compromise earth continuity from equipment in DB 2 back to MSB.
This follows a principle set in IEC 60364 (in which "3000" is based); that once the combined functions of the PEN of a TN-C system have been separated into the separate N & PE functions of a TN-S system . they must not be re-combined at any point downstream.
In NZ (& Oz); we use TN-C for distribution networks, with incoming mains PEN to MSB (including MEN link).
At MSB, the combimed N & PE functions are separated, with PECs from that point on not being allowed to carry load current, and the N generally having no PE function.
-----
An alternative view is that connection of a PEN outgoing submain to a DB supplied by separate N & PE conductors is prohibited.
That view is based on the OEC principle; and may well have been the intent of this rule.
However the wording of Clause 5.5.3.1 in "3000" does not specifically prohibit this practice, it on;y reqiores that any 'cascaded' PEN must not depend for its continuity on terminals of an intermediate swbd.
And this requirement clearly applies regardless of whether the first submain is PEN or N+PE.
So not correct to say: "on a PEC submain, and the outgoing PEN neutral can be connected to the neutral bar as normal".
Doing so would make the (earth) continuity of the PEN dependent on terminal(s) of the intermediate DB
In every case of an outgoing PEN, from a DB, it must be connected directly to incoming N-conductor.
What the clause does do is restrict this cascading to outbuildings only.
It is NOT compliant to originate a PEN submain at a DB of the main building.
We can take the PEN submain from MSB, or we can take it from an outbuilding.
Option B is that supply to the outbuilding DB is via one or more other DB that are in other outbuildings, and not direct from MSB.
Noting that there is no valid option of supply via DBs in main building, only via DBs in other outbuildings.
Keeping it simple; we have new OB 2 supplied by Submain 2 which is fed from DB1 in OB1, which is fed from MSB.
(v) applies to the PEN conductor of (new) submain 2 to OB2.
It requires that continuity of the PEN must not rely on any terminals of DB1.
So correct that, at DB1, if the incoming submain 1 supplying DB1 has a PEN; then the outgoing PEN of submain 2 cannot be connected to N-bar of DB1, but instead must be connected directly to incoming N of submain 1; with a tee-off to the N-bar of DB1
In Slovett's case, the incoming submain 1 to DB1 is not PEN, but instead has separate N + PEC.
Item (v) says nothing about whether (intermediate) DB1 is fed with a PEN or by a N + separate PEC, so same rule applies.
So in this case also the outgoing PEN of submain 2 cannot be connected to N-bar of DB1, but instead must be connected directly to incoming N of submain 1.
A PEN conductor serves 2 separate and distinct functions.
as an N conductor, it has to carry return / out-of-balance load current.
As a PE conductor, it has to carry earth fault currents and also equipotential bonding.
It's this PE function that can't be compromised by being disconnected at DB1.
All points required to be earthed must have continuity at all times back to main earthing terminal at MSB.
If the outgoing PEN of submain 2 is connected to N-bar of DB1, then disconnection of either that connection , or of the incoming N of submain 1, would compromise earth continuity from equipment in DB 2 back to MSB.
This follows a principle set in IEC 60364 (in which "3000" is based); that once the combined functions of the PEN of a TN-C system have been separated into the separate N & PE functions of a TN-S system . they must not be re-combined at any point downstream.
In NZ (& Oz); we use TN-C for distribution networks, with incoming mains PEN to MSB (including MEN link).
At MSB, the combimed N & PE functions are separated, with PECs from that point on not being allowed to carry load current, and the N generally having no PE function.
-----
An alternative view is that connection of a PEN outgoing submain to a DB supplied by separate N & PE conductors is prohibited.
That view is based on the OEC principle; and may well have been the intent of this rule.
However the wording of Clause 5.5.3.1 in "3000" does not specifically prohibit this practice, it on;y reqiores that any 'cascaded' PEN must not depend for its continuity on terminals of an intermediate swbd.
And this requirement clearly applies regardless of whether the first submain is PEN or N+PE.
So not correct to say: "on a PEC submain, and the outgoing PEN neutral can be connected to the neutral bar as normal".
Doing so would make the (earth) continuity of the PEN dependent on terminal(s) of the intermediate DB
In every case of an outgoing PEN, from a DB, it must be connected directly to incoming N-conductor.
What the clause does do is restrict this cascading to outbuildings only.
It is NOT compliant to originate a PEN submain at a DB of the main building.
We can take the PEN submain from MSB, or we can take it from an outbuilding.