Hi Eng-Tips Electrical Community,
This is my first post though I'll admit I've been a ghost-reader for some time. Many thanks for all the helpful posters I've benefited from in the past.
I'm an electrical engineer working on a low voltage transformer secondary cable application and am seeking advice on cable ampacity as per the CEC.
Details:
- 600V, 3 wire.
- Single core TECK90, sheaths bonded at source only.
- Run Length: 10m
- Non-ferrous gland plates to be used at entries.
- Blocking spacing for short circuit forces (to be determined).
- Required ampacity: 2000A
- Proposed configuration: 4 per phase 1c500MCM in trefoil arrangements (each ABC) with 1 cable diameter spacing between cables, and 2 cable diameter spacing between trefoil groups.
Question:
I'm unclear on the application of Table 1 ampacities as they relate to parallel runs of single conductor cables. The appendix for rule 12-108 indicates that a trefoil configuration (cores touching) for each per phase conductor will allow for even splitting of current between the parallel cores (see figure B12-1). However, the appendix notes that the configurations shown may not always result in equal current division, with little explanation. Moreover, I'd prefer to space the cables in each trefoil by 1 cable diameter to take advantage of full single core ampacity if possible. However, I'm not clear if this has an impact on the mutual inductance between each trefoil. Some other references indicate that no more than one cable diameter spacing in trefoil, should still result in relatively even current division between parallel sets, but the CEC is silent on this. (or is it?). I could also do a two layer configuration that is also purported to lead to equal current division (other references), but that would require a derating for layering, which I can infer from table 5d, but for which I don't believe there is an obvious rule.
Parallel sets of single core cables are done so often in industrial applications that I'm thinking I may be missing something. I'd expected the CEC to provide a straightforward method for installation method and derating requirements for single core parallel installations. Am I missing something obvious? I just completed a Neher McGrath calculation for another project, and I'm trying to avoid the complexity and cost by hopefully applying the CEC alone.
Sincere Thanks,
Justin
This is my first post though I'll admit I've been a ghost-reader for some time. Many thanks for all the helpful posters I've benefited from in the past.
I'm an electrical engineer working on a low voltage transformer secondary cable application and am seeking advice on cable ampacity as per the CEC.
Details:
- 600V, 3 wire.
- Single core TECK90, sheaths bonded at source only.
- Run Length: 10m
- Non-ferrous gland plates to be used at entries.
- Blocking spacing for short circuit forces (to be determined).
- Required ampacity: 2000A
- Proposed configuration: 4 per phase 1c500MCM in trefoil arrangements (each ABC) with 1 cable diameter spacing between cables, and 2 cable diameter spacing between trefoil groups.
Question:
I'm unclear on the application of Table 1 ampacities as they relate to parallel runs of single conductor cables. The appendix for rule 12-108 indicates that a trefoil configuration (cores touching) for each per phase conductor will allow for even splitting of current between the parallel cores (see figure B12-1). However, the appendix notes that the configurations shown may not always result in equal current division, with little explanation. Moreover, I'd prefer to space the cables in each trefoil by 1 cable diameter to take advantage of full single core ampacity if possible. However, I'm not clear if this has an impact on the mutual inductance between each trefoil. Some other references indicate that no more than one cable diameter spacing in trefoil, should still result in relatively even current division between parallel sets, but the CEC is silent on this. (or is it?). I could also do a two layer configuration that is also purported to lead to equal current division (other references), but that would require a derating for layering, which I can infer from table 5d, but for which I don't believe there is an obvious rule.
Parallel sets of single core cables are done so often in industrial applications that I'm thinking I may be missing something. I'd expected the CEC to provide a straightforward method for installation method and derating requirements for single core parallel installations. Am I missing something obvious? I just completed a Neher McGrath calculation for another project, and I'm trying to avoid the complexity and cost by hopefully applying the CEC alone.
Sincere Thanks,
Justin
