Oven Replacement - RCD?

[lozarus]

Afternoon all. Apologies if this is a stupid question. I'm currently half part way through completing 2391 (second exam tonight) - so may be getting myself in a tiz overthinking things.

Either way, thought I'd put it out to the group.

Task is: Straight swap of existing x5 ovens with new - "like for like", if you will. Albeit cooker plate to appliance is also in T&E and I intend to replace this with a more suitable product - namely HO7.

Earthing arrangement is: TN-S.

Environment is: Educational establishment, cookery rooms.

Circuits for the room originate in a local 3P+E MEM2 board, no RCD's. Ovens are simply domestic 1P+E bog standard, cheap household jobs, wired from C32's at the DB to 45a Isolators (no socket) at each station, cooker outlet below. Room is only about 10m long.

EICR from 2020 is available, but quite a few tests missed out - IE: Zs for each oven measured well within limit. No IR or R1+R2 undertaken - I'll be doing this anyway. It's all PVC T&E - mainly in metal trunking. I think it's loose behind the cabinets for the last few metres however.

My big question here is RCD. I could take the "like for like" approach and just straight swap the ovens out as "maintenance". But the environment (education) makes me think I really should be pushing for RCD's.

Further to this, manufacturers instructions state "Additional protection by RCD is recommended".

With that in mind, I'm convincing myself these really should be going onto RCD shouldn't they?

Or convince me I'm wrong. Sorry if I've overcomplicated a simple job here.

Thanks.

 

[brianmoooore]

If you're quick enough with the megger after the RCD trips, you will see a rapidly increasing resistance. The resistance when measured cold is orders of magnitude higher than when the hot element trips the RCD. Presumably caused by the element moving by expansion/contraction.
On the type of elements we are discussing, the live and neutral terminals have a foot or so of element between them, so L - N shorts aren't normally possible.
I was around long before RCDs, and it wasn't at all unusual to see holes blown in the outer sheath of these elements, or even severed completely.