Double Cable Protection Question

The problem is that each of your 240mm2 cables is only rated at 550A at most, so if (due to accident or error) a situation arose where only one of the 4 conductors was connected, the 830A breaker would offer no protection.

it is an MDP supplying a sub Distribution panel 120 meters away from MDP. The MDP has a main ACB rated @2500 amps, 4P, 400 Volts supplying 3 MDP in 3 different location. The design load of the sub MDP we are discussing now is 900 Amps @ 400 V. MY main question is? is it really required by the new code like IEC or BS or NEC? these 3 codes is the only code recognize by our local authority and insurance company w/c insured our equipment.

Ask your consultant to provide you with excerpts from the IEC standard he is refering to.

Parallel conductors are meant to provide an alternative to a single conductor of the required size.

That is the first question I asked him. But his answer is the latest revision and he cant remember the iec number and cenelec number. thank you and when he visit here again I will show him your reply.

I can't follow any rational logic to doing something like that.

Given that if the multiconductor service has a dedicated CB for each run of cable it would make no sense simply do to that in order to turn off the line multiple independent breakers would not only have to be tripped but be interlocked so that if one trips they all go off line together.

I think your consultant is misunderstanding a code or is just blowing smoke up your backside to make himself feel important.

Setting up such a system would be a huge waste of main panel space and financial cost.

The codes do address one problem in parallel cables and circuit breakers. The CB should be set to trip on short circuit (not load) for only one of the cables. There is also a section that indicates that the use of parallel cables should be only used for voltage drop purposes, not for load carrying. Some individuals might interpret that to indicate that the breaker should be set for the load capacity of only one cable, but the use of 2 or more cables in parallel is done frequently assuming that both cables are carrying 1/2 of the load for 2 in parallel, etc. I can see that in some jurisdictions an inspector might give a problem but I think the consultant is simply inexperienced. However do note that the short circuit settings and calculations should be done for a single cable. That is usually no problem when 1-4 cables are in parallel. When more are used some people use CT's on each cable or groups of cable. One way to provide load protection for each cable is to put separate CT's on each cable and separate relays to limit the load, but I have never seen that done except by Utilities.

This makes no sense! How are you going to connect the 1600 amp breaker to the 830 amp breakers? How are you going to reestablish the 1600 amps on the other end? Like others have said, get someone more qualified to help you!