Control Panel wiring questions

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NetNathan

Net is where I be and Nathan is me
Location
Corona, CA
Occupation
Mgr. Electrical and Controls Eng
1. Is there a minimum wire size I can use?
My I/O is all fused at 10 Amps and I want to use 16 AWG.
I thought somewhere I read that 14 AWG was the minimum wire size.

2. Can I pull MTW in a conduit?
 
NetNathan said:
1. Is there a minimum wire size I can use?
My I/O is all fused at 10 Amps and I want to use 16 AWG.
I thought somewhere I read that 14 AWG was the minimum wire size.

2. Can I pull MTW in a conduit?
Click to expand...

Does this control panel consist of at least one of the sections below?

Industrial Control Panel. An assembly of two or more
components consisting of one of the following:

(1) Power circuit components only, such as motor controllers,
overload relays, fused disconnect switches, and
circuit breakers

(2) Control circuit components only, such as pushbuttons,
pilot lights, selector switches, timers, switches, control
relays

(3) A combination of power and control circuit components
These components, with associated wiring and terminals,
are mounted on or contained within an enclosure or mounted
on a subpanel. The industrial control panel does not include
the controlled equipment.
Click to expand...

If so you are going to want to read article 409. Section 409.110 may be hard for you to comply with.
 
This is my layout...
3. A combination of power and control circuit components
These components, with associated wiring and terminals,
are mounted on or contained within an enclosure or mounted
on a subpanel. The industrial control panel does not include
the controlled equipment.


But....
409 does not give me minimum wires size.
409.110 is marking...how will this be a problem?

No mention of uses for MTW (I know I can use in control panel but can I run in conduit?)
 
Last edited:
There is no mention of allowed uses for MTW because it is not a recognized NEC Chapter 3 wire type. You have to use it where NEC does not apply or look at the additional wire type listings for the same wire.

Sent from my XT1585 using Tapatalk
 
14ga is minimum for FIELD wiring to devices. Internal to a control panel, it's what the circuit protection device allows. 16ga = 10A, you are good to go.

MTW is INTENDED to be used inside of appliances, machines and control panels. Most people consider that not suitable for pulling in conduit, it's easy to damage the insulation and the high strand count to be flexible results in a slightly higher risk of it breaking when being pulled. THHN/THWN is essentially MTW + a nylon coating to protect it when pulling through conduit, in fact you will often see that THHN with higher strand count is also cross listed as MTW. Both are listed in 310.104 as "suitable for all uses described..."(sic). But what you will notice is that MTW is not included in the conduit fill tables in Chapter 9. You can still use it, you just have to manually calculate your fill rates based on the specific outside diameter of your MTW.
 
GoldDigger said:
There is no mention of allowed uses for MTW because it is not a recognized NEC Chapter 3 wire type. You have to use it where NEC does not apply or look at the additional wire type listings for the same wire.

Sent from my XT1585 using Tapatalk
Click to expand...
No, it's there... at least in the 2011 code. 310.10. The ampacity is not shown, but there is an Informational Note in 310.15.1(A) saying you can find it in NFPA79
 
I don't plan on pulling MTW in conduit now. It is thicker and I like the cover on THHN for pulling...it also moves way easier in the conduit due to its covering.
But if my wiring is fused at 10 amps, I should be able to run 16 for PLC IO....plus my PLC outputs are fused at 2 amps) in the control panel, in the conduit to the equipment junction box, and from there to the devices... no motors.
 
NetNathan said:
1. Is there a minimum wire size I can use?
My I/O is all fused at 10 Amps and I want to use 16 AWG.
I thought somewhere I read that 14 AWG was the minimum wire size.

2. Can I pull MTW in a conduit?
Click to expand...
Of course in doing this type of work you do have a copy of NFPA 79, Electricsl Standard for industrial Machinery publcation. It should address the questions that you have about control panel wiring.
The MTW question should be addressed in the NFPA 79 code book regarding raceways.
 
NetNathan said:
No mention of uses for MTW (I know I can use in control panel but can I run in conduit?)
Click to expand...
.
i've done a fair bit of control work, and i've used #14 MTW for control circuits, pulled
in conduit.

i've also seen an awful lot of #16 MTW pulled in raceways for pilot duty. it's not legal,
but it gets done a lot, factories being what they are, and changes made in systems
that will never get inspected by anyone, ever.
 
NetNathan said:
1. Is there a minimum wire size I can use?
My I/O is all fused at 10 Amps and I want to use 16 AWG.
...
Click to expand...
Please refer to Article 725 for specifics, especially for Class 2 and 3 circuits which may permit as small as 22AWG.

725.43 Class 1 Circuit Overcurrent Protection. Overcurrent
protection for conductors 14 AWG and larger shall be
provided in accordance with the conductor ampacity, without
applying the ampacity adjustment and correction factors
of 310.15 to the ampacity calculation. Overcurrent protection
shall not exceed 7 amperes for 18 AWG conductors
and 10 amperes for 16 AWG.

Exception: Where other articles of this Code permit or
require other overcurrent protection.
Informational Note: For example, see 430.72 for motors,​
610.53 for cranes and hoists, and 517.74(B) and 660.9 for​
X-ray equipment.​
Click to expand...
725.49 Class 1 Circuit Conductors.

(A) Sizes and Use. Conductors of sizes 18 AWG and
16 AWG shall be permitted to be used, provided they supply
loads that do not exceed the ampacities given in 402.5
and are installed in a raceway, an approved enclosure, or a
listed cable. Conductors larger than 16 AWG shall not supply
loads greater than the ampacities given in 310.15. Flexible
cords shall comply with Article 400.

(B) Insulation. Insulation on conductors shall be rated for
the system voltage and not less than 600 volts. Conductors
larger than 16 AWG shall comply with Article 310. Conductors
in sizes 18 AWG and 16 AWG shall be Type
FFH-2, KF-2, KFF-2, PAF, PAFF, PF, PFF, PGF, PGFF,
PTF, PTFF, RFH-2, RFHH-2, RFHH-3, SF-2, SFF-2, TF,
TFF, TFFN, TFN, ZF, or ZFF. Conductors with other types
and thicknesses of insulation shall be permitted if listed for
Class 1 circuit use.
Click to expand...
 
Thanks Smart $.

And From NFPA 79...

12.6.2 Conductors shall not be smaller than 16AWG for lighting
and control circuits conductors on the machine and in
raceways or 18 AWG where part of a jacketed, multiconductor
cable assembly.
 
I've been using a lot of #16 lately for my control circuits. I keep the #16 mtw in the control panel/plc cabinet and use #16 tffn stranded for the field wiring.
 
I know it is said that 14 awg is minimum for field wire devices but consider that many devices today are wired to M12 connectors, a lot of which have molded cables attached.
Usually these are 22 awg which is suitable for the typical device being used. But then these circuits are not fused at 10 amps, these will be fused at 4 amps or less.
 
Aleman said:
I know it is said that 14 awg is minimum for field wire devices but consider that many devices today are wired to M12 connectors, a lot of which have molded cables attached.
Usually these are 22 awg which is suitable for the typical device being used. But then these circuits are not fused at 10 amps, these will be fused at 4 amps or less.
Click to expand...
Most of the time when something is connected with an M12 connector or similar system, you will find that they are SUPPOSED to be fed by a Class 2 power supply. I'm not saying that always happens, I'm saying the mfrs of the devices that come with an M12 connector do a CYA by putting that in the instruction sheet or some engineering document somewhere.
 
Jraef said:
Most of the time when something is connected with an M12 connector or similar system, you will find that they are SUPPOSED to be fed by a Class 2 power supply. I'm not saying that always happens, I'm saying the mfrs of the devices that come with an M12 connector do a CYA by putting that in the instruction sheet or some engineering document somewhere.
Click to expand...

Where I work that is the case. Usually this will just be a larger power supply bussed into fuses limited to 4 amps or less, keeping us below the 100VA level. Smaller machines and systems may use
a Class 2 supply, if the 100VA will be enough. Otherwise you would need multiple supplies to run a large system.
 
NetNathan said:
This is my layout...
3. A combination of power and control circuit components
These components, with associated wiring and terminals,
are mounted on or contained within an enclosure or mounted
on a subpanel. The industrial control panel does not include
the controlled equipment.


But....
409 does not give me minimum wires size.
409.110 is marking...how will this be a problem?

No mention of uses for MTW (I know I can use in control panel but can I run in conduit?)
Click to expand...
If you are making the panel for a customer they may have a specification for minimum conductor size.
 
templdl said:
Of course in doing this type of work you do have a copy of NFPA 79, Electricsl Standard for industrial Machinery publcation. It should address the questions that you have about control panel wiring.
The MTW question should be addressed in the NFPA 79 code book regarding raceways.
Click to expand...

Or UL508A. They are similar. Both cost $$$ and I agree having a standard is important
 
First, you need to determine what the local authorities will have to say about your panel. Often if it is shown to be UL or compliant with a particular NFPA, they will let it go but they have the ultimate say so.

As mentioned previously, you should look at NFPA 79. There are provisions for all types of wiring, particularly for wires for signalling and data, where power is not involved.

And this: 7.2.4.2.2 “Control circuit conductors sizes of 18, 16, and 14 AWG shall be considered as protected by an overcurrent device(s) of not more than a 20-ampere rating.” Make sure you know what a "control circuit conductor" is before you apply that too broadly.
 
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