electricalforum.nz

Just wanting some thoughts on the origin of the FSC for EVSE. The first quote below is from the addendum to the work safe guidelines and the second from AS/NZS 3000:2018.

“3. Where an EVSE is installed at a residential installation, the charging final subcircuit shall be protected by a type B RcD and the subcircuit shall originate from a MEN switchboard.”

“7.9.2 …The supply shall NOT be obtained from a switchboard that is supplied by a PEN neutral conductor in the submain using the outbuilding provisions of Clause 5.5.3.1. NOTE: The use of the PEN neutral and earth connections required for electric vehicle charging system prevents the correct earthing connections from being provided for the electric vehicle charging system earthing failure detection system.”

So the work safe guidelines recommended the FSC coming from an MEN switchboard, but 3000:2018 requires that it is not supplied by a sub board with a PEN.

Is there a reason that EVSE should be supplied by an MEN board or would it be fine to supply from a sub board with a submain PEC? And if it should be supplied by an MEN board then would all EVSE FSCs need to be supplied from the main switchboard?

I realise these documents are not mandated through the regulations, but would still need to base electrically safe reasoning off of something.

Because I don't have a strong knowledge of EVs I'm sure there is a reason for the clauses above

"NOTE: The use of the PEN neutral and earth connections required for electric vehicle charging system prevents the correct earthing connections from being provided for the electric vehicle charging system earthing failure detection system."

The above seems to indicate why for one of those scenarios

I wouldn't install anywhere other than a MSB with the information currently provided

It's easy enough to work through and so comply with both;
at least in theory.

the Guideline quoted requires supply from an MEN swbd.
There's no definition for this term any more; but can only mean one with an MEN link.
In 1993 & 1997 Regs was defined as having both an MEN link and an MEC to an electrode;
- but that definition was revoked when ESRs came into force in 2010.

The clause in "3000" requires not from an MEN swbd that is in an outbuilding.
Note this applies to ALL EV circuits; not just domestic.

For domestic; the combined effect is that the EV circuit must originate at MSB
Which is completely impracticable of the domestic installation in question is a block of flats;
as the EV circuit for a 4th-floor flat's dedicated carpark in basement can't come from that flat's swbd, but instead must come from the MSB.

For non-domestic; the requirement to come from a MEN swbd does not apply, so supply from a DB will comply,
regardless of whether the DB in question has a link, and regardless of whether the earth of the submain is PEN or PEC.

Electrically there's NO difference between earthing arrangements for domestic vs non-domestic installations.
If supply from a DB is OK for non-domestic, it must be equally OK for domestic.
And since every set of mains is PEN, there's not a lot of difference between an MSB and a MEN swbd in an outbuilding.
Which suggests that the stated reason is more waffle than fact.
As does the fact that the guideline (which was written later) doesn't include this particular restriction

Guideline 1.4 (d) requires the charger to have an earth continuity monitoring system.
Short of a dedicated earth electrode, this can only be done by monitoring the continuity of the N-E lop of the FSC, and any submain, back to the N-E link (All EV supplies must come from a TNCS source; so there will always be a N-E link upstream).
The N & E will always show up as pretty much a dead short, impedance varying slightly with cable route distance between the N-E connection and the charger.
The earth continuity monitor may well react to excessive impedance, as against simply open circuit.
But it can't tell what's caused the impedance, and there can be no difference to the impedance based on whether the MEN link is in an outbuilding or not.

Ignore my reference to earth monitoring requirement; it's for monitoring the earthing connection to the vehicle.
But I still see no good reason for either the guidelines' requirement for supply from MEN swbd or the '3000" requirement for not-from-outbuilding MEN swbd.

I thought the requirements seemed a little unnecessary, so thanks for the input in working through it.