Fuses, sized correctly, are always better protection than C/Bs. If they fail, they will always fail-safe, unlike a C/B (A C/B may not work when you need it).
The right type of fuse will have greater fault protection capability than a C/B. However, fuses must be replaced each time they open, while C/Bs can be reset.
Aside from choice of overcurrent protection, if this is for a safety-related stationary application—please, take my word for it—specify closely monitored high-grade current and voltage bird-dogging for the pair. [Was party to one $30-miilion “oops/oversight.”]
Suggestion: Fuses can be better designed for the low peak protection than circuit breakers since the magnetic operation of the CB tends to be slower than the melting operation of the low peak fuses. However, the DC circuit breakers are faster than AC circuit breaker.
Addition to my previous post and following on busbar's concern: battery chargers also commonly have failure alarm functions (local and/or dry contact for remote signaling). Opertion of internal overcurrent protection would activate the alarm function if present. External overcurrent protection devices would need some type of alarm circuit to indicate failure.
144x, a curious question.
Any C/B can only open when current flow through it exceeds its settings.
If you mean will it open for current flow in either direction, the answer is yes.
If you mean will it open for a fault upstream that no current through it is feeding, the answer is no.
You are absolutely correct that many chargers have current limiting on their rectifiers, which offers some degree of protection against a fault, but is mainly there to restrict the maximum charging current and to prevent the rectifier melting when charging a depleted battery. The current limit does not reduce the available fault from the battery itself, just limits the contribution from the charger.
Most industrial batteries can deliver a fault current far in excess of the charger which feeds them. It would be hazardous to omit a protective device in the battery circuit itself, regardless of whether the charger has a limit or not. Large DC batteries are worthy of respect.
ScottyUK - Your points are valid, but the question pertained to the protection between the charger and the battery, not between the DC bus and the load. In addition to current limiting most chargers are equipped with output fuses or circuit breakers.
My comment was based on a situation where cabling or busbar between the battery and the charger was damaged, or the charger suffered an internal failure. The battery would feed into the fault in both these situations if there was no fuse or CB for the charger (unless the battery has its own fuse or CB)
I'm used to seeing the charger located in close proximity to the battery rack. The charger nomally has an output breaker or fuse (with monitoring). If there is a a significant length of wiring between the battery and charger or distribution panel, OC protection at the battery would be appropriate.
actually the problem started when a contractor refused to install the fuse box between charger and battery and proposed to use MCB installed in charger instead.I was not feeling easy with this as I was afraid of accepting the risk of autoamtic tripping of MCB for what ever reason other than fault.in that case you would not have either charger or battery and there is also no alarm to notify you of the problem .
MCB in DC circuit is a difficult (may be more expensive)proposition, especially if the battery AH rating is high. It is the practice to provide Fuse box close to the battery terminals to isolate the battery quickly for any external faults. I have seen the battery cells explode.
In charger, the MCB is always on the AC input supply side and includes auxiliary contacts to monitor its status. The point where the battery supply is paralleled with the charger supply and then passed to the DC distribution board, there is no additional switchgear.
The above I wrote from experience with large lead acid batteries of 1000AH and more and hope will be of use to you.
Suggestion: Traditionally, DC circuit breakers are in minority, when it comes to their applications. The circuit breaker DC ampere contact rating is often somewhat questionable, set somewhat empirically, and lower in comparison to AC applications of the AC circuit breaker.
