Conduit Fill Calculation Using Multi-Conductor Tray Cable

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krneison

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I would like for someone to clarify the calculation involved in figuring out conduit fill using multi-conductor tray cable.

The way I understand it as it is stated in Chpt. 9, note 9 in the notes to the tables we use the 53% fill column from the appropriate catagory as it is treated as a single conductor. The area where I get confused is that it states in note 9 that we base the calc on the major diameter of the cable. Does that mean that we use the value given by the manufacturer of the wire and compare that to the appropriate 53% fill column or do we take the diameter (pi*rsquared) of that given value from the wire manufacturer and use that answer to compare?????

ex: A #6 Southwire 3c THHN/PVC, GW, TYPE TC POWER CABLE
It's ave. overall diameter in inches is .71(as per Southwires tables); The prints tell me to pull it into a 1" EMT conduit which is .458". To me this says a NO GO and I need to upsize to an 1 1/4". Or do I take the diameter calc of
.71" which is .3959" and I can use the 1" EMT.

Please Help :-?
 
krneison said:
I would like for someone to clarify the calculation involved in figuring out conduit fill using multi-conductor tray cable.

The way I understand it as it is stated in Chpt. 9, note 9 in the notes to the tables we use the 53% fill column from the appropriate catagory as it is treated as a single conductor. The area where I get confused is that it states in note 9 that we base the calc on the major diameter of the cable. Does that mean that we use the value given by the manufacturer of the wire and compare that to the appropriate 53% fill column or do we take the diameter (pi*rsquared) of that given value from the wire manufacturer and use that answer to compare?????

ex: A #6 Southwire 3c THHN/PVC, GW, TYPE TC POWER CABLE
It's ave. overall diameter in inches is .71(as per Southwires tables); The prints tell me to pull it into a 1" EMT conduit which is .458". To me this says a NO GO and I need to upsize to an 1 1/4". Or do I take the diameter calc of
.71" which is .3959" and I can use the 1" EMT.

Please Help :-?
Click to expand...
The fill thing is cross section area. A cable with a diameter of .71" has a cross sectional area of 0.40". The ID of the conduit would need to be > 0.98" to meet the 53% requirement.
 
krneison said:
I would like for someone to clarify the calculation involved in figuring out conduit fill using multi-conductor tray cable.

The way I understand it as it is stated in Chpt. 9, note 9 in the notes to the tables we use the 53% fill column from the appropriate catagory as it is treated as a single conductor. The area where I get confused is that it states in note 9 that we base the calc on the major diameter of the cable. Does that mean that we use the value given by the manufacturer of the wire and compare that to the appropriate 53% fill column or do we take the diameter (pi*rsquared) of that given value from the wire manufacturer and use that answer to compare?????

ex: A #6 Southwire 3c THHN/PVC, GW, TYPE TC POWER CABLE
It's ave. overall diameter in inches is .71(as per Southwires tables); The prints tell me to pull it into a 1" EMT conduit which is .458". To me this says a NO GO and I need to upsize to an 1 1/4". Or do I take the diameter calc of
.71" which is .3959" and I can use the 1" EMT.

Please Help :-?
Click to expand...

The last sentence refering to the 1"EMT is correct. However make sure that the fittings (if) you use allow sufficient beding radius to install the TC. The fittings are often the determining factors of what size you will select, or you can use UP/DOWN reducers with the smaller conduit. (Makes for an ugly insrtallation.)

IMO TC does not belong into conduit of any kind, it defeates the primary purpose of using conduit, not to mention the high likeliness of damaging it during pull.. When it's outside of the tray, use wirebasket or channel.
 
weressl said:
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IMO TC does not belong into conduit of any kind, it defeates the primary purpose of using conduit, not to mention the high likeliness of damaging it during pull.. When it's outside of the tray, use wirebasket or channel.
Click to expand...
I have worked in a couple of plants where conduits were run from the tray to the motors or other equipment. The conduit runs were fairly short, less than 30' or so, and used to provide support and physical protection of the TC. Is this not a common installation?
 
don_resqcapt19 said:
I have worked in a couple of plants where conduits were run from the tray to the motors or other equipment. The conduit runs were fairly short, less than 30' or so, and used to provide support and physical protection of the TC. Is this not a common installation?
Click to expand...

That's quite common, but also expensive. Using the wire tray or channel where allowed by code is more flexible (easier to change) and can be less costly than individual conduit runs from tray to motors and equipment. A major chemical company with many, many motors did research at their plants and determined there are less failures running tray cable than using conduit. Conduit brought moisture into the motor junction box. A cable gland and a drip loop in the cable kept the water out and led to fewer motor failures, according to their survey. They used non-armored TC cable with minimal mechanical protection from the tay to the motor.
 
don_resqcapt19 said:
I have worked in a couple of plants where conduits were run from the tray to the motors or other equipment. The conduit runs were fairly short, less than 30' or so, and used to provide support and physical protection of the TC. Is this not a common installation?
Click to expand...

It is common, but it does not exclude it from being less than optimal. Unless you have an assembly type plant, where the machinery lines up in a neat 'row', then the location of equipment will be more random. In that case the runs would be most likely longer, unless you have cable tray running al over whoch would defeat its main benefit, eg. you use tray where you would 'bank' your conduits.
 
Volta said:
Welcome to the forum!

Yes, your last calc is good, the diameter of a .71 cable is allowed in any conduit except PVC sched 80, which would need to be 1.25".
Click to expand...
Thank you! Looking forward to using the forum. It's already working for me. So you are stating that taking pi*radius squared of the given overall diameter off the manufacturers table is the correct way to get the cross-sectional area?
 
rcwilson said:
That's quite common, but also expensive. Using the wire tray or channel where allowed by code is more flexible (easier to change) and can be less costly than individual conduit runs from tray to motors and equipment. A major chemical company with many, many motors did research at their plants and determined there are less failures running tray cable than using conduit. Conduit brought moisture into the motor junction box. A cable gland and a drip loop in the cable kept the water out and led to fewer motor failures, according to their survey. They used non-armored TC cable with minimal mechanical protection from the tay to the motor.
Click to expand...

It's common practice in the semi-conductor plant I work in.
 
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