How to calculate number of cores for control cables?

[eemamedo]

What is the proper way to calculate number of cores for control cables? For power cables it is quite straightforward: 3 for balanced load, 4 for unbalanced (3 + N). However, is there a rule of thumb for control cables?

Appreciate the help.

 

[don_resqcapt19]

No rule of thumb for control cables. The number of conductors needed is based on the control scheme being used or the device that the control cable is connected to.

 

[gadfly56]

Welcome to the forum!

Добро пожаловать на форум !

(Here's hoping Google Translate didn't mangle that too badly, my last Russian Level 2 class was 40+ years ago.)

 

[Jraef]

I always add 25% spares. Sometimes people complain about the added cost, but nothing is more expensive than having to pull it again because you find out you need 3 more wires.

 

[Besoeker]

What is the proper way to calculate number of cores for control cables? For power cables it is quite straightforward: 3 for balanced load, 4 for unbalanced (3 + N). However, is there a rule of thumb for control cables?

Appreciate the help.

It isn't a calculation. It's a count. As in count how many you need then add some spare capacity.

 

[gadfly56]

I always add 25% spares. Sometimes people complain about the added cost, but nothing is more expensive than having to pull it again because you find out you need 3 more wires.

A couple of companies ago, my boss would have us run 4-conductor FPLP for every circuit, even though it needed only two. I asked why, and he said "What happens if there's a short or open in one of the conductors? This way I have spare conductors no matter what. Wire is cheap, labor is expensive." I still remember that 16 years later.

 

[petersonra]

I agree that spares are a wise thing to include.

 

[iwire]

Pull spares, tell no one.

When spares are needed charge for installing them.

 

[Jraef]

Pull spares, tell no one.

When spares are needed charge for installing them.

:thumbsup::thumbsup::thumbsup:

 

[eemamedo]

I always add 25% spares. Sometimes people complain about the added cost, but nothing is more expensive than having to pull it again because you find out you need 3 more wires.

I see... What I did was the following. I have a schematic and I counted how many cables will be coming in and out (counted for Emergency push button). I got 4 so I wrote 5 to have one extra. I looked at couple of catalogs and noticed that some of them have standard number of cores. E.g. Abhar wires uses 5, 7, 8 cores, so I think I should keep that in mind when I make a cable schedule. Of course, different vendors will have different standard cores but it should be close to each other.

 

[petersonra]

I see... What I did was the following. I have a schematic and I counted how many cables will be coming in and out (counted for Emergency push button). I got 4 so I wrote 5 to have one extra. I looked at couple of catalogs and noticed that some of them have standard number of cores. E.g. Abhar wires uses 5, 7, 8 cores, so I think I should keep that in mind when I make a cable schedule. Of course, different vendors will have different standard cores but it should be close to each other.

With this kind of cable it is often cost effective to buy all one size. So even if you only need 4 or 5 wires to a particular spot, it might be overall more cost effective to just make it all 15 or 20 conductor, or whatever works out best, rather than having shorter lengths of different sizes. plus it is simpler to order one size rather than 3 or 4. And there is little chance of someone running the wrong cable since they are all the same.

 

[Besoeker]

I always add 25% spares. Sometimes people complain about the added cost, but nothing is more expensive than having to pull it again because you find out you need 3 more wires.

We quite often got specs, particularly for petrochem projects, where 25% spare capacity for control conductors and terminals was mandated.

 

[Tony S]

Our company only stocked 4 types of control cable, 7, 12, 19 and 27 core 2.5mm² SWA. You used the next size up to what you needed. But if say a 27 core would be more than 75% utilized two 19 core would be pulled in. (I wasn’t pulling the cables so it didn’t bother me.)

As with any multinational, trying to order something not on the standard approved list was a nightmare.