Power point in external glasshouse

[cliffed]

Client wants 2g socket in greenhouse, obviously IP rated,will be supplied from Rcd, the greenhouse consists of metal frame work on the ground.
Does this require MPBC

 

[LastManOnline]

It an extraneous & needs bonding with the appropriate sized conductor

For the illustration you posted supplementary bonding would suffice. The drawings replicates how a kitchen sink was traditionally bonded to the socket where the electric kettle was plugged in

 

[mainline]

For the illustration you posted supplementary bonding would suffice. The drawings replicates how a kitchen sink was traditionally bonded to the socket where the electric kettle was plugged in

Just wondering how you would connect the bonding

 

[LastManOnline]

Just wondering how you would connect the bonding

As the OP describes the installation, there are no extraneous parts except for the metal frame. Makes bonding very simple. The metal frame will provide a path to earth but it will likely be relatively high resistance (should be tested and established). A bonding conductor of 4mm from the socket to the metal frame will be more than adequate.

 

[mainline]

As the OP describes the installation, there are no extraneous parts except for the metal frame. Makes bonding very simple. The metal frame will provide a path to earth but it will likely be relatively high resistance (should be tested and established). A bonding conductor of 4mm from the socket to the metal frame will be more than adequate.

Maybe it's not a good idea to export the PME to the metal frame ?

 

[pc1966]

It is really about the relative risks of each of the options:

• TT avoids the whole open-PEN fault issues of high touch potential and possibly high sustained currents in the CPC irrespective of RCD/MCB protection. But in turn you are dependent on the RCD electronics and light-current trip mechanism to disconnect on any fault.
• TN gives you the reliable high fault current option to disconnect on the OCPD side of things, but in turn you have the issue of differences in CPC/Earth potential leading to the issue of bonding of extraneous parts, etc, open-PEN magnitudes of currents, etc.

In this situation I would probably go with TT due to the 2*1.5mm CPC of the supplying RFC and what that could mean for open-PEN faults. Though I would be tempted to put a RCD style socket as TT on the existing socket's supply so no single RCD failure for anyone plugging stuff in.

 

[mainline]

It is really about the relative risks of each of the options:

• TT avoids the whole open-PEN fault issues of high touch potential and possibly high sustained currents in the CPC irrespective of RCD/MCB protection. But in turn you are dependent on the electronics and light-current trip mechanism to disconnect on any fault.
• TN gives you the reliable high fault current option to disconnect on the OCPD side of things, but in turn you have the issue of differences in CPC/Earth potential leading to the issue of bonding of extraneous parts, etc, open-PEN magintude of currents, etc.

In this situation I would probablygo with TT due to the 2*1.5mm CPC of the suppling RFC and what that could mean for open-PEN faults. Though I would be tempted to put a RCD style socket as TT on the existing socket's supply so no single RCD failure for anyone plugging stuff in.

Agreed, TT is the way to go.

 

[pc1966]

As the OP describes the installation, there are no extraneous parts except for the metal frame. Makes bonding very simple. The metal frame will provide a path to earth but it will likely be relatively high resistance (should be tested and established). A bonding conductor of 4mm from the socket to the metal frame will be more than adequate.

That is one aspect that never seems to be covered as "extraneous conductive" could range from sub-ohm with seriously high open-PEN currents being possible (e.g. metallic service pipes shared with other DNO circuits) to the kOhm range when any mechanically sound bond wire will do.

I guess the old 10mm, etc, rule is about assuming the worst (but still realistic) case.

 

[LastManOnline]

I guess the old 10mm, etc, rule is about assuming the worst (but still realistic) case.

Completely agree. In the domestic sector "bonding" and "10mm" have become synomimous. Interchangeable. Causing unfortunately a lot of confusion and unnecessary expense in the process.
Take this particular post for example. Its revolved around whether the OP should run a 6mm or a 10mm main bond?. In reality, neither a 6 or 10 mm is required.
Unfortunately the regulators have inadvertently created a situation where the confusing issue of bonding, which causes so many headaches, looks set to continue causing headaches for the next generation of sparks

 

[cliffed]

Agreed, TT is the way to go.

Agree TT is the way, it’s been a epic post with many points of view.
This just proves that adding a power point to the greenhouse needs a lot of thinking & cost wise, gonna be expensive.
The client literally told us how to connect the power, from an existing external socket.
Shes in for a surprise when priced for TT system, Rcd DB, etc

 

[pc1966]

Agree TT is the way, it’s been a epic post with many points of view.
This just proves that adding a power point to the greenhouse needs a lot of thinking & cost wise, gonna be expensive.
The client literally told us how to connect the power, from an existing external socket.
Shes in for a surprise when priced for TT system, Rcd DB, etc

So are the existing sockets not on RCD at all?

If they are on DP RCD/RCBO then all it needs is the local earth rod (and I presume bonding that to the greenhouse frame).

I don't have amendment 2 book yet, but have they allowed the RCD socket outlets to be used again for "additional protection" and/or what other restrictions are still in place for that?