origin of the installation

This rather depends on the supply impedance - what you are really saying is the company fuse can clear a modest L-N fault (over-current may or may not be dead short) in 5 seconds or so but not an fault to earth in 0.4 or 0.2 seconds. On a TT supply this situation is definitely true and an RCD or earth fault relay is needed at the origin. With a TN-s or TNC-s supply it may well be true that a short L- CPC would clear the fuse. However, it needs some measurement/ analysis and may or may not need something on the customer side to protect that sub-main across the car-park.
Mike

thanks, Mike

It's a TNS system from a distributor's breaker, well above 63A, and I think that the cable across the car park would be classed as a distribution circuit. Would that require a disconnection time of 5s for a L-CPC short?

I'm probably splitting hairs but, assuming that we can get the clearance time down to whatever the right level is, do the wiring regs allow us to use the distributor's protective device to provide protection against electric shock by automatic disconnection of supply? I'm concerned about the lack of a specific provision in the regs, when such provisions are made for protection against overcurrent

Dave 

Has anyone checked what the supplier deems acceptable?  I have no idea about industrial installations, but a couple of hundred hards of buried cable protected only by the supplier's fuse wouldn't be accepted on a domestic install.

thanks, Simon

since the supply regs changed in 1988, I'm not sure that the supplier/distributor can mandate what happens after their protective device. I have seen some long runs of 25 SWA and even bare wire overhead protected only by a cut-out fuse

Dave

Well they can refuse a new supply, and generally do round here, with anything more than about 3m of anything after their fuse, although another fuse of the same value seems to make them happy despite really adding nothing to the breaking characteristics. ...
The installation has to be a lot worse to justify disconnection of an existing supply however, which is probably good, as there are a lot of dodgy looking set ups that predate the current regime 

In the end its the DNO's call, and will depend a bit on the opinion of the local area chaps.

Mike.

thanks, Mike

I'm sure I can talk the distributor around, but I'm still concerned about making sure that this installation complies with the wiring regs. specifically, I need to clarify what clearance times the regs require for protection against electric shock by ADS (following your earlier comment) and whether the regs allow use of the distributor's protective device to achieve such ADS

if there's another way to make the installation safe and demonstrate compliance with the wiring regs for protection against electric shock, then I'd welcome any suggestions

Dave

Who owns the substation/transformer?

I am wondering how this is different from the couple of hundred yards of street main and service cable from the transformer, which is a couple of doors away from my house.

the difference, and therefore perhaps the issue, is who owns that couple of hundred yards of cable

the supply to your house is through cables owned and operated by the distributor (therefore governed by supply regs rather than wiring regs) to a cut-out in your property. the origin of your installation is a few feet of double-insulated tails from the cut-out through the meter to your DB

for the project I'm working on, the distributor's responsibility ends at a metered breaker in the substation. the origin of this installation is a couple of hundred yards of cable across the car park to the main DB

Dave Miller said:

for the project I'm working on, the distributor's responsibility ends at a metered breaker in the substation. the origin of this installation is a couple of hundred yards of cable across the car park to the main DB

Then the origin is at the metered breaker (in the substation).

for the project I'm working on, the distributor's responsibility ends at a metered breaker in the substation.

ah. That you did not mention.  Then everything from then on is yours to use for ADS or not as you think suitable at your risk.
Mike.