protection against a utility company bolted fault
protection against a utility company bolted fault
(OP)
some assistance, please, on basic electrical principles:
why does all the electrical equipment (say in a residential building) such as service switches and panelboards need to have a greater ampere interrupt capacity (AIC) than the utility company maximum symmetrical short-circuit current bolted fault rating?
why can't a service switch (which is on the line side of the panelboards) with a very high AIC be enough to handle the utility company bolted fault?
why does all the electrical equipment (say in a residential building) such as service switches and panelboards need to have a greater ampere interrupt capacity (AIC) than the utility company maximum symmetrical short-circuit current bolted fault rating?
why can't a service switch (which is on the line side of the panelboards) with a very high AIC be enough to handle the utility company bolted fault?






RE: protection against a utility company bolted fault
RE: protection against a utility company bolted fault
i'm finally understanding this. ok, so i need to change the circuit breakers in the main distribution panel. how do i prove this will clear the the bolted fault condition?
RE: protection against a utility company bolted fault
e.g. - the available short circuit current is 15,000 A, symmetrical and all of your breakers are rated for 22,000 A. This is acceptable. If you have one breaker rated for 10,000, that's a problem.
BTW, the term "bolted fault" is just referring to a fault with no impedance at the fault ( a zero ohm fault).
RE: protection against a utility company bolted fault
The utility contribution is only how much "juice" the utility will "pour in" to the system under a fault condition. In general (and I do mean in general)...the farther the fault location is away from the utility (in feet of copper), the less the max fault value due to impedance of transformers, copper (or aluminium) wire, etc... Bear in mind....I just made a VERY simplied and general explaination. I've done calcs where utility contribution might be 2k, but way downstream the fault value might be less than a hundred amps. Basically means you can install cheaper protective equipment the farther downstream you go.
RE: protection against a utility company bolted fault
respectfully
RE: protection against a utility company bolted fault
This rating represent the largest potential short circuit current which can occur in the location of selected application imposing severe mechanical forces and thermal stresses in the breaker, panel, cables and other circuit components.
If the available short circuits at the location of the panel exceed the SC rating of the assembly, the entire installation is exposed to fire, smoke, explosion and other hazard conditions. See sample of possible hazard conditions
For additional information in this topic see the enclose bulleting.
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RE: protection against a utility company bolted fault
My Refrigeration buddy told me about an experience like your righthand picture. He was working a large control panel that ran a cooling tunnel in our local gummy bear factory. They control the temperature of the tunnel by staging refrigeration compressors. Eight six cylinder compressors. They bang another one on as demand increases. Well he was working away and 6 were on. Then 7 went on and he noticed some warmth down by his feet but didn't actually connect it with anything. Then the eighth one went on and an orange glow appeared and lit up his boots. He looked and the line feeding all the contactors was glowing. It had long ago vaporized its insulation.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com