Door Earthing - Low voltage (LV) Panel

The code applicable to the country of installation is the first port of call.

If in doubt, consult a qualified local Electrical Engineer.

I am completely ignorant in this area, so I am replying in an attempt to educate myself more than anything else.

First in reply to the other two replies: I think the original poster is happy that his panel meets local standards, but, wants to understand why the door earth is allowed to be such a small gauge.

To the OP when you say "4P + E", do you mean 3 phase + neutral + earth?

I would guess that if any of the live wires gets shorted to the door then the small earth wire will easily carry enough current to trip any earlier safety device.

What you are referring to is an equipment ground.

The main equipment ground must be sufficient to trip the main supply breaker in the event of a fault to the equipment or conduit.

It is sized by the main breaker capacity.

The entire panel should be at equipotential.

The door will have some connectivity to the panel via hinges,locks,etc,but that cannot be relied upon for safety.

The size of the bonding jumper is usually designed by the manufacturer or site engineer.

Here is a link with many more details on all types of electrical bonding. :.

https://www.electricianinformationresource.com/electrical-bonding.html

It would be pointless for the <...cable size for Panel Door earthing...> to be greater than the cross-sectional area of the <...Panel Door...>, allowing for the possibility of different materials being used for them...

"Not knowing exactly what to say,I said nothing" Mark Twain

The CSA of the door is also irrelevant.

IP40 and above are going to have polymer door seals. The only earth circuit will be through the catch and hinges. The CSA of the catch and hinges in powder coated steel with poor contact points is likely to have a much higher resistance (Ω) value than 2.5mm² copper wire. Where the door was large enough to have three hinges and multipoint catches we always earthed the doors at both top and bottom. CSA of the door is irrelevant.

Must be an echo in here.

As pointed out above, local guides/standards/codes will apply, and I also agree with the comment regarding 2.5mm sq. as a minimum for simple mechanical strength for bonding, increased as required for the supply.

That said, it may be useful to consider the method of attachment to the door. Traditionally we would always use M6 minimum (again for strength) and if in doubt test it. We did tests at 50kA prospective (415V), using 100A fuses to prove our connection was sufficient and did not blow itself off under fault conditions (Icc test). This was a dead short to the door so very extreme and unlikely. The connection method compared to a 16mm sq. equivalent.

Not all studs are created equal, and they are known to be a weak point amongst test engineers.....