The insulation has to sustain the highest voltage the cable will face under normal conditions. How short period of time are we talking about?
Ask the cable manufacturer of the cable you're planning on using.
They have the last say in what their cable can and cannot handle.


As for the load, with a 2A current pretty much ""anything"" will suffice.
0,75mm2 and up. That's not a lot of current. But another thing you have to factor is that the wire gauge and length will also affect the short circuit currents that will be induced in the event of a short.
You're not giving me alot to work on.

Does intended operating voltage (ie below 825VAC) qualify as ""normal"" conditions?

The cable is connected to a power supply with a dial that adjusts the voltage applied, and as such it is possible that operator increases output by inadvertently. I'd expect this to be corrected as soon as operator is made aware of the mistake but who is to say if we're talking 5 seconds or 2 minutes?

We did ask manufacturer of a cable rated 450/750 and in our setup the rating can be superseeded to 825VAC (Ref EN-50565-1, part 1 table 2)

It seems this would suffice for our intended purposes but since it is possible to exceed the approved voltage using a dial there is a concern regarding safety and the regulatory requirements.

We're using 2.5mm2 and I believe this is well beyond the requirements for a short, also considering that there are fuses in place?

The output is in RMS, I presume this goes for AC rating as well?

Is there any other information you need in order to determine required cable rating?

On a side note, We've also looked into using a voltage triggered circuit braker in order to prevent voltage output exceeding approved limits but have yet to find one. Suggestions would be welcome :)

Normal conditions would be the highest voltage setting you can achieve without modifying it in any way. We always have to account for the human factor when deciding on cables and equipment. There is no way around it I'm afraid.

If the dial goes way beyond the voltage rating of the cable I would say that this is not good. You may know the limits of this setup personally and use it in a controlled and safe manner, but would you trust the operators knowledge on the matter? I certainly wouldn't. It may be for a minute or it may be for six hours.
The bottom line is that it has to be foolproof.

The same principle applies when chosing cable gauge for a power outlet for example. You would never protect a 1,5mm2 cable feeding an outlet with a 16A fuse. Since this should be protected with a 10A fuse. Because you never know what other people would do and you have no control.

I admit I don't have any first hand experience when it comes to exceeding insulation ratings on cables and what rules that applies, as I have always worked on fixed voltages(230 and 400V where the cable rating on the cables far exceeds that). It has never been an issue.

In practice I THINK you would be safe as cables are stress tested by the manufacturer using far higher voltage levels.
But you're pretty much a test pilot when exceeding the limits the manufacturer has certified it to. And you have to guarantee its safe operation under all circumstances upon completion. It's more a question of responsibility and keeping within the standards than what will likely happen.

I'm sorry if I couldn't give you a better answer

Hello Jan,

On one hand you are stating that we have to account for human factors and that the system has to be foolproof. From a safety point of view, as well as the explicit and underlying intention of standards and regulations, there is no way around this.

On the other hand you are ambiguous since you also suggest that it might not only be ok to exceed cable voltage rating but also that it may be deemed safe.

Have I understood you correctly?

Since I have no prior experience with cable voltage ratings I would very much appreciate if someone could provide clear instructions regarding cable voltage rating requirements.

Using the cable rated 450/750 as an example, as well as a 1000VDC/1400VAC test setup would be much appreciated.

The way I understand the 450/750 rating is that no more than +-450V relative to ground is allowed on a single conductor, several conductors with +-450V would result in a maximum voltage difference between conductors of 900V. Therefore, in order not to exceed the rating the max applicable voltage on this cable would be +-375V on several conductors, and +-450 if on only one conductor.

This is confusing to me since standard EN-50565-1, part 1 table 2, allows for slightly higher voltages (825VAC in this case) than those the cable are rated for under the condition that it is a single phase system.
A single phase system on cable would imply that there is one phase with an oscillating voltage, connected to Neutral through the load. The max potential between ground and phase can not exceed 480V (as stated in standard). It is therefoe not possible to attain 825V between conductors in a single phase system?
In a multi phase system this is achievable, as described in my take on the 450/750 rating, but the exception where it is permitted to exceed the rating, as stated in the standard, requires that it is a single phase system.

What am I missing here, and what cable voltage rating is required for a 1000VDC/1400VAC [test] system?

Kind regards,
Niklas

Correction:

Exceeding the 450/750 rating as per EN-50565-1 part 1 table 2 is not conditional on using a single phase system. It was a subnote intended only for cables rated 300/300.

It makes sense now ,)

I'm answering on generic terms.

My point boiled down to, yes, it MIGHT be absolutely safe for all we know. Or maybe not.
After all, cables are really put to the test by the manufacturer for good measure.
But you can't put it on paper officially as you have little control of the outcome.
You cannot guarantee the safety. Maybe this proves to be dangerous after a given period of time in over voltage conditions where the insulation eventually breaks down. See where I'm going?

You have to be 100% sure.

Stick within the limitation brought on by the manufacturer to keep your hands clean. Or you bear the full responsibility and have to answer for what can potentially happen.

I would be very carefull and hesitant going down that road.

A two tonne chain might be able to carry a 2,5 ton load. But how can you be sure of that? What are you going to do when it snaps and the load falls on someone? The manufacturer of the chain surely will not take the blame for it. The same with the cable manufacturer and maximum rated voltage. You will be the guilty part and no one else.

It's entirely your call but be aware of the risks and responsibilities you are taking here.

I don't know how I can clarify any further. I think it sounds sketchy. You simply don't exceed the limitation of anything unless given a green light from the respective manufacturer. This being volts, amps, tonnes or anything.

Only the cable manufacturer can give you a valid answer to these questions.

And for what? To cut costs on the choice of conductors?
Is it worth the responsibility and risk?

I don't mean to sound harsh. I'm just pointing out that building electrical systems is based on a chain of responsibilities. From the manufacturers and down to the one building it.
And you're breaking that chain by exceeding the limits, so all responsibilities falls on you.

Jan,

I know the cable I used as an example has a voltge rating that under any circomstance is way below that wich is to be deemed safe and legal.

In order to provoce a clarification on what goes and what doesn't I had to ""advocate"" both sides. We will not install mentionen cable.

However, while trying to define the specifics of what voltage rating a cabel has to have with regards to the intended purpose I have encountered several arguments. Therefore it would be nice to be able to say that for any and all intended purposes, a cable with voltage rating x has to be used where max conceivable potential is lower than x, as per this or the other regulation.

While we are both right, it would be nice to prove it.

Surprisingly, i have to say, few seem to be able to answer the very basic (!?!?) question of: What cable rating [u] is to be used when? And then they refer to cable manufacturers who rated the cables.

I thought this was clearly regulated and specified in standards so that an electrician tasked with selecting a cable would know what cable would be acceptable without having to contact several manufacturers and ask them what the particular cable ratings mean.

I do appreciate you trying to help me out here.