If the source impedance is low (such as a battery bank) short circuit current can be huge. AC breakers fail as well as DC. When the utility company improved their pole pigs a lot of fires resulted.
As a result the code was changed that fuses were required on any load above 2 horsepower. Thus your central air has a fused disconnect.
Terrible helpless feeling to watch a meltdown and unable to stop it. A fuse is much cheaper than a new boat or house.
May you be in heaven a half hour before the Devil knows your dead.
From: Tom <boat_works@yahoo.com>
To: electricboats@yahoogroups.com
Sent: Friday, September 23, 2011 10:17 PM
Subject: [Electric Boats] Over-current protection
To: electricboats@yahoogroups.com
Sent: Friday, September 23, 2011 10:17 PM
Subject: [Electric Boats] Over-current protection
The Oct/Nov issue of Professional Boatbuilder magazine has an article on
the design and installation of large battery banks.
In a side bar, the author discussed protection of large banks with Wayne
Kelsoe, VP of electrical engineering at Blue Seas Systems. Among the
author's conclusions is that Class-T fuses are preferred over circuit
breakers for protecting large battery banks.
..."a common failure mode after a short-circuit fault is for the
contacts to fuse when reset. How many of us have reset a circuit breaker
without investigating the cause? If the fault still exists, and the
over-current protection is compromised, a fire could result. At the very
least, the breaker will be internally damaged, and will not reset,
allowing the circuit to remain open. Boat operators often carry spare
fuses, but how many carry spare primary circuit breakers?"
Anybody in the group had any experience with the type of circuit breaker
failure that Wayne is talking about?
-Tom
the design and installation of large battery banks.
In a side bar, the author discussed protection of large banks with Wayne
Kelsoe, VP of electrical engineering at Blue Seas Systems. Among the
author's conclusions is that Class-T fuses are preferred over circuit
breakers for protecting large battery banks.
..."a common failure mode after a short-circuit fault is for the
contacts to fuse when reset. How many of us have reset a circuit breaker
without investigating the cause? If the fault still exists, and the
over-current protection is compromised, a fire could result. At the very
least, the breaker will be internally damaged, and will not reset,
allowing the circuit to remain open. Boat operators often carry spare
fuses, but how many carry spare primary circuit breakers?"
Anybody in the group had any experience with the type of circuit breaker
failure that Wayne is talking about?
-Tom
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