When You Need It
- · A cable specification has to be justified against the network fault level
- · The screen or sheath cross section has been proposed by a manufacturer and needs checking
- · Protection settings have changed and the clearance time is no longer what the cable was sized for
- · An earth fault return path runs through the screen and its capacity has never been confirmed
Standards Applied
IEC 60949IEC 60287BS 7430EN 50522
The report states the clause and the edition it works to, so the calculation can be reproduced by whoever reviews it.
What You Get
Conductor and screen short circuit withstand for the stated fault level and duration
The minimum acceptable screen cross section, and whether the proposed one passes
The fault level and clearance time used, with their source named rather than assumed
Earth conductor sizing on the adiabatic basis, for both copper and aluminium
Where the clearance time comes from a relay we have not set, a statement of what the calculation depends on
Try It Yourself First
Frequently Asked Questions
Do you need the protection settings to do this?
We need the clearance time. If the settings exist we will use them, and if they do not we will state the time assumed. It is the single input most likely to make the answer wrong, so it never gets buried.
Can you do the earthing calculation alongside it?
Yes. Earth conductor sizing on the adiabatic basis, and the screen as a fault return path, are the same family of calculation and are usually worth doing together.
The Rest of the Cable Chain
Review, calculation, drawings, testing and fault location, from one place. See the whole picture.