S
skatingsparks
Hello there
This question is from my Design and verification course notes(sample question)
An industrial heating load is supplied at 400V, 50 Hz by a multi core armoured cable with copper conductors and 90 degree C thermosetting insulation. The circuit is controlled by a fuse switch fitted with BS 88-2-1 fuses rated at 100A. The ambient temperature along the route of the cable is 30 degrees. and installation is method C. The declared value is of Ze is0.35 ohms
a calculate the minimum CSA of a separate protective conductor(copper) to be installed for this circuit, in order to satisfy thermal and shock constraints.
b Describe briefly how to determine the CSA of the cpc to be installed other than by calculation method
c Explain why the CSA of the cpc in a may differ to that in b.
The only way i can see to work this out is to use the adiabatic equation. I assume that that the disconnection time is 5 seconds(because is above 32 amps) with a 100 A fuse and according to Fig 3.3B the time current curve for BS 88 that for a 5 seconds disconnection time the fault current will need to be 550A . the k factor for that the cable is 143 from table 54.2.
Put that lot in the adiabatic and i get 8.6. so use a 10mm
Well thats how I interpreted the question anyway.
Sound ok or is there another way of working that out that i can't see as I am blind from studying to much. why are they telling me the Ze. Can't work out the Zs as length of cable isn't know.
For b is just said use table 54.7. But for that i had to assume(lots of assumptions) that 25mm cable was used. Got that assumption from table 4E4A, method C, 1 three or 4 core cable. Can't be 16mm, next size up 25mm.
Fair assumption, to many assumptions??
c Table 54.7 work on worse case scenario
Any thoughts.?????
Half the problem is understanding what's been asked not the actual question.
Thanks
skatingsparks
This question is from my Design and verification course notes(sample question)
An industrial heating load is supplied at 400V, 50 Hz by a multi core armoured cable with copper conductors and 90 degree C thermosetting insulation. The circuit is controlled by a fuse switch fitted with BS 88-2-1 fuses rated at 100A. The ambient temperature along the route of the cable is 30 degrees. and installation is method C. The declared value is of Ze is0.35 ohms
a calculate the minimum CSA of a separate protective conductor(copper) to be installed for this circuit, in order to satisfy thermal and shock constraints.
b Describe briefly how to determine the CSA of the cpc to be installed other than by calculation method
c Explain why the CSA of the cpc in a may differ to that in b.
The only way i can see to work this out is to use the adiabatic equation. I assume that that the disconnection time is 5 seconds(because is above 32 amps) with a 100 A fuse and according to Fig 3.3B the time current curve for BS 88 that for a 5 seconds disconnection time the fault current will need to be 550A . the k factor for that the cable is 143 from table 54.2.
Put that lot in the adiabatic and i get 8.6. so use a 10mm
Well thats how I interpreted the question anyway.
Sound ok or is there another way of working that out that i can't see as I am blind from studying to much. why are they telling me the Ze. Can't work out the Zs as length of cable isn't know.
For b is just said use table 54.7. But for that i had to assume(lots of assumptions) that 25mm cable was used. Got that assumption from table 4E4A, method C, 1 three or 4 core cable. Can't be 16mm, next size up 25mm.
Fair assumption, to many assumptions??
c Table 54.7 work on worse case scenario
Any thoughts.?????
Half the problem is understanding what's been asked not the actual question.
Thanks
skatingsparks
