Permissible load of redundant 63A and conductor cross-section

Dear forum users.

In order to make sure about the competence of the electrician who will perform installation work for me, I would like to ask a few things:

1. With a 63A three-phase circuit breaker, what maximum device power can I connect between the individual phases? (all devices will be powered between phases 400V), I mean maximum use of protection, i.e. devices will be connected between phases: 1 and 2, 2 and 3, 1 and 3.

2. What cross-section should be used for the cable (length approx. 20-30m) in the case of 63A three-phase protection, assuming that only 400V devices will be used?

Thanks in advance for your advice.

hazaj wrote:

What cross-section should be used for the cable (length approx. 20-30m) in the case of 63A three-phase protection, assuming that only 400V devices will be used?

There is no single table of long-term load capacity of cables, but there are tables le. They indicate the permissible load capacity depending on the type of environment and the number of cables laid together. We don't have that information here. In any case, the necessary cross section is 10 or 16 mm square.
However, the cross-section of the wires does not only depend on the long-term load capacity. The allowable voltage drops and short-circuit loop impedance must also be calculated. And only all these factors determine the selection of the cross-section, and the as-built measurements are to confirm the accuracy of the selection.

Col. hazaj- in the subject: A few words about the protection of installations, motors, and RCDs
there is a table - from "roughly" you can deduce something

Thanks for your comments, I'm correct.

The cable will be 5-core (YKY) laid in the ground.

I have a table where the permissible load of 35A is given for a cross-section of 6mm2.

Do I understand correctly that when the device is powered at 400V, 35Ax400V = 14kW will come out?

Hello. You might like this:

Regards.

hazaj wrote:

The cable will be 5-core (YKY) laid in the ground.

Then don't skimp on the cross-section, just use 5 x 25 mm Al (YAKY) and you'll still have cheaper. And why 5-wire and not 4-wire?

Thank you guys for the entries, but unfortunately no one was tempted to give a specific answer to specific questions.

So, let me ask the question a bit differently:
Q1 If we have a 63A overcurrent fuse, does that mean the maximum load for each phase or the total load for all phases?

Q2. If we are to protect devices with a total power of 20kW, then use a 63A protection, or is 40A enough?

Thanks in advance for specific answers.

1. Per phase 63A
2. Nobody knows. Because it doesn't bode well from coffee grounds, you just need to know the nature of the load. It's different for engines than it is for bulbs.

hazaj wrote:

Thank you guys for the entries, but unfortunately no one was tempted to give a specific answer to specific questions.

This protection 63A is supposed to be some kind of protection:
- against short-circuit,
- against overload,
- shock protection,
- power limiting device.

This is a specific question

hazaj wrote:

Q2. If we are to protect devices with a total power of 20kW, then use a 63A protection, or is 40A enough?

It's about a "resistive" load, more precisely about resistance heaters.
Generally, the assumption was that there will be 4 heaters with a power of 5kW each, but to make the load even, we are considering using 6 heaters with less power and evenly connecting the individual phases.

answer one more question: is it for residential or business purposes? If the latter, I really advise you to spend money on the project, because there will be problems, and not small ones. And in the event of an accident, the prosecutor will not be lenient. I've cited investigation cases on the forum several times. And then there's the issue of insurance. No company will pay a penny of compensation if there is no documentation approved as God has commanded.

Generally, it is a heating installation on the premises of the company. An electrician was commissioned to install such an installation (but in order to install it, he has to distribute the lines supplying the individual heaters from the switching station). Is it therefore within his scope of responsibility to carry out the project? Should an electrician come "ready", i.e. get a project and do everything according to the project?

hazaj wrote:

Generally, it is a heating installation on the premises of the company. An electrician was commissioned to install such an installation. Is it therefore within his scope of responsibility to carry out the project? Should an electrician come "ready", i.e. get a project and do everything according to the project?

An electrician should get a project and do everything exactly with the project!!!
Well, unless the electrician has a building license in the field of designing electrical installations, he can do the project himself. For a separate fee of course. It's just that designers very rarely "dirt" their hands with personal workmanship (it's like the designer of the building transporting bricks to the bricklayer in wheelbarrows). And after the work is completed, the electrician should take measurements and draw up a report. And the owner (manager) of the facility is obliged to keep a complete set of documentation and present it to the inspection authorities. And there are many of them, from the National Labor Inspectorate, through the Fire Service, to Building Supervision. I don't think I need to mention the annual and five-year reviews.

P.S. What if there is no change in the use of the facility? If yes, then the installation project has to approve the fire safety appraiser And you should expect an inspection from the building supervision.

Kol. hazaj - in the third post I gave you a link to the topic in which you have many things explained. There is also a table (even two) with cross-sections of wires and cables for which protection is selected. The last item in the first table (column D- for cables laid in the ground) and the values given for 2 and 3 (two loaded cores or 3 loaded cores). On the basis of the load capacity, the cross-section of the wire / cable can be selected - but this is not the only criterion. There are others that raise the bar even further (permissible voltage drop, short-circuit loop impedance, stacking factor...).

Quote:

Is it therefore within his scope of responsibility to carry out the project? Should an electrician come "ready", i.e. get a project and do everything according to the project?

As kol. retrofood wrote - you need the appropriate permissions, which your electrician probably does not have. I know cases where a project was requested (with a positive result) for power supply and installation in a garage with a total power of 10kW.

Thank you so much friends for all the information, which is extremely helpful to me.

In principle, the question was only about the cross-section and protection, but in the end we came down to the issue of permissions. Therefore, I have a question, is a project prepared by a person with building qualifications in the field of designing electrical installations required for each extension of the electrical installation?

Therefore, if, for example, I want to install an additional electric heater at home or in my company, to which I have to connect the power supply from the switchboard and install a separate fuse, do I need to have a project first? How are these regulations? Are there any conditions by which to determine whether a project is required or not?

Well, following this lead, when connecting every heater, boiler, oven or other electrical device, a project would be needed ... And we know perfectly well that when connecting this type of device, the services of an electrician are rarely used, not to mention a designer.

It is understandable that the connection should be made by a licensed electrician, but is a project necessary right away?

These matters are regulated by the Construction Law and the Regulation of the Minister of Infrastructure of 12 April 2002 on the technical conditions to be met by buildings and their location. (Journal of Laws of 2002, No. 75, item 690).
The law distinguishes two types of works: renovation, i.e. restoring the original state, and reconstruction, i.e. adding something new. And while during the renovation, solutions that met the requirements of the regulations from the construction period can be used, during the reconstruction, it is necessary to adapt to today's standards and regulations.
Now for the projects. A blueprint is required for each redevelopment. I was designing the electrical installation for the guest's porch lighting (one light bulb, one switch), because a Building Permit was required for the construction of this porch, and without the installation design, the County Office did not issue such a permit. Of course, when the whole thing does not require a construction project, someone does not do the project privately, because no one sees the point.
But companies are not doing so well. Companies are subject to many controls and sooner or later someone will ask for such documentation. Let, for example, an employee get burned. There will be an investigation immediately: who and when designed the heating, did he sign that it was in accordance with the regulations, who performed it? Did it perform as designed? And did the employee have the right to be here at that time ... I would not like to be in the shoes of the owner, who then will not have documentation.

Referring to this topic, I would like to ask one more question.

If we have the following situation


||||||||||||||||||||| --------------------------------- L1
||||||||||||||||||||| 8kW heater (powered by 400V)
||||||||||||||||||||| --------------------------------- L2


In the above situation, the current is 8000W/400V=20A
Therefore, L1 and L2 carry a current of 20A? I mean, should the power cable L1 and separately L2 be adapted to a load of at least 20A (i.e. each wire with a cross-section of 2.5mm2)? Or should a single wire be rated for 10A?

hazaj wrote:

Therefore, L1 and L2 carry a current of 20A?

Well, unfortunately yes.

that is, both the L1 and L2 wires must be selected for the current of 20A (i.e. each of them must have a cross-section of at least 2.5mm2)?

hazaj wrote:

that is, both the L1 and L2 wires must be selected for the current of 20A (i.e. each of them must have a cross-section of at least 2.5mm2)?

In this case - yes.

Thank you.

So if the following situation happens:
- connecting three heaters with a power of 3.33kW (8.33A) - powered by 400V, with symmetrical division into 3 phases, is a 5x6mm power cord enough? - at a length of 20-30 m?

Can two such systems (on two separate power cables) be connected to the 40A protection, or is 63A necessary?

hazaj wrote:

Thank you.

So if the following situation happens:
- connecting three heaters with a power of 3.33kW (8.33A) - powered by 400V, with symmetrical division into 3 phases, is a 5x6mm power cord enough? - at a length of 20-30 m?

No, my friend is having fun with this 6mm?. After all, if you connect these heaters in a triangle ?, the 2.5mm? cable will still have a spare.

I'm not kidding, just asking. I'm not an electrician, so I don't know. However, the opinions of electricians who are supposed to connect me are different, so I allowed myself to ask on the forum.

So if we connect 3 heaters with a power of 3.33kW powered by phase-to-phase voltage in a triangle, then a cable with a cross-section of 2.5mm2 (with a length of 20-30m) will be enough?

And what about the selection of protection, when powering 6 such heaters, also connected in a triangle?

hazaj wrote:

....So if we connect 3 heaters with a power of 3.33kW powered by phase-to-phase voltage in a triangle, then a cable with a cross-section of 2.5mm2 (at a length of 20-30m) will be enough?

totally.

hazaj wrote:

... And what about the selection of protection, when powering 6 such heaters, also connected in a triangle?

In short, it should be selected so as to protect against the effects of short circuits, overloads and ensure SWZ, for example S303 B20A for each such set. However, it should be supported by measurements.

Thank you very much for all the information, there is nothing like the opinion of an expert.

What exact measurements in this case (in terms of protection selection) should be made by an electrician?

Whatever he measured and did there, he owes you an electric shock protection report. And it is your responsibility to have such protocols.