Allowed Volt drop in a Cable run

<...that do not effects the system...>

....is meaningless. Provided the conductors are not superconductors, there will always be a voltage drop while current is being carried. The question as posted is unanswerable.

Please refer to the latest edition of the Wiring Regulations, published by the IET. Within its pages are many algorithms for the correct selection of cable size.

In Canadian Electrical Code book there is an eg; on Table D4 on Voltage Drop, I don't have NEC that I can refer too.

The post is not unanswerable. Increase the conductor size to acomodate the voltage drop!

It totally depends on both the system, and the applied voltage.

Every system is different. Even two circuits made by the same company will have different actual operating tolerances.

What system are you powering? What is its input power requirements and tolerances? It is normally on a label on the system.

Is 415V constant? Is it actually 415V

The power lines feeding the circuits will also use power (combination of resistance of the wires and the connections)

The votage drop across any conductor is dependant on the the current flowing through it and its resistance. So you need to know the maximum current your system will be drawing and refer to latest edition wiring regs for the size of cable you require. If you did not already know this, I would advise leaving the 415 Volts alone in case you fry yourself!

In the UK the wiring regs require 4% max volt drop but you ask what is maximum voltage drop - this is determined by the equipment you are powering at the other end of the wire i.e. if your equipment is rated for 400V +/- 20% then you can drop 20%.

This is regarding the consumers actually.

I have not realized more than +/-20%.

I have to ask this question!

Why would you risk unpowering any equipment? The cost of replacement from overheating a motor and other problems.

Spend the money to supply more power than needed will actually save moeny in the long run!!!!!!!

The standard answer in the USA is maximum of 3% measured at the last out. There isn't a National Electrical Code requirement...it's just good engineering practice.

hmm, i've studied a bit more and found these:

1,5% for internal lighting installations

3% for internal power -motors etc- installations

5% for external installations.