Batteries- fused?
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websparky
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Re: Batteries- fused?
lbartsch,
This may apply to your question. Hope it helps!
lbartsch,
This may apply to your question. Hope it helps!
Dave
Re: Batteries- fused?
No, fuses are not required in the battery strings, and highly discouraged. They are only used if AHJ demands them. It takes training and special equipment to replace fuses in battery strings. If fuses are replaced improperly it will damage the equipment and cause long-term outages which cannot be tolerated.
[ June 29, 2003, 11:05 PM: Message edited by: dereckbc ]
No, fuses are not required in the battery strings, and highly discouraged. They are only used if AHJ demands them. It takes training and special equipment to replace fuses in battery strings. If fuses are replaced improperly it will damage the equipment and cause long-term outages which cannot be tolerated.
[ June 29, 2003, 11:05 PM: Message edited by: dereckbc ]
Re: Batteries- fused?
dereckbc,
I tend to agree with websparky on this issue. Article 480 is very clear about this and states very clearly that wiring and equipment shall be subject to the requirements of CODE. There is nothing else that I can see that nullifies this.
I have a Bell System power background and we never used them in central offices, yet, I believe that they should be mandatory. There is a high leverl of fault current available from these battery strings and with then number of strings they are installing in parallel, I can't see how, as good engineers, we can permit not using them.
dereckbc,
I tend to agree with websparky on this issue. Article 480 is very clear about this and states very clearly that wiring and equipment shall be subject to the requirements of CODE. There is nothing else that I can see that nullifies this.
I have a Bell System power background and we never used them in central offices, yet, I believe that they should be mandatory. There is a high leverl of fault current available from these battery strings and with then number of strings they are installing in parallel, I can't see how, as good engineers, we can permit not using them.
ron
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Re: Batteries- fused?
It is a great idea to follow the code, although the phone companies do not have to. Somehwat similar to the power companies utilizing some other magical Table for their wire sizing.
It is a great idea to follow the code, although the phone companies do not have to. Somehwat similar to the power companies utilizing some other magical Table for their wire sizing.
Re: Batteries- fused?
Ahhh! article 90 rears its ugly head. I have to agree that article 90 applies technicaly, but I have yet to find an AHJ that will accept it.
I contacted NFPA a while back and asked them just what constitutes a utility. They indicated that any company recognized by the AHJ as such (a very subjective answer).
Lets assume that they get away with it and do not have to use NEC, what standard do they use? Telcordia? Their own internal standard? I'm all for article 90 if the company has something else of substance to use.
Ahhh! article 90 rears its ugly head. I have to agree that article 90 applies technicaly, but I have yet to find an AHJ that will accept it.
I contacted NFPA a while back and asked them just what constitutes a utility. They indicated that any company recognized by the AHJ as such (a very subjective answer).
Lets assume that they get away with it and do not have to use NEC, what standard do they use? Telcordia? Their own internal standard? I'm all for article 90 if the company has something else of substance to use.
Re: Batteries- fused?
Generally a utility is any company recognized by a city, municipality, state or local government. This is usually done by elections granting the company a monopoly. As a utility they are not required to apply for building permits nor are they ever inspected by an AHJ
As a former SWB and MCI CO power engineer of 24 years all Telco?s has debated this topic several times over the last 100 years. It really comes down to company policy. Most decide not to fuse battery strings because of the outage potential created, complexity in replacing the fuse, and the minimal risk involved.
There are two NEC code issues widely ignored by telephone companies where DC power is involved. One is fusing battery strings; the other is a de-rating conductor for adjustment factors of 310.15.B.2 contained in raceways.
SWB and MCI policy is not to use any fuses in battery strings in central offices. However there are special circumstances where they will be used such as CPE (customer premises equipment) where the facility is not owned or maintained by the Telco, or in co-located facilities where Telco does not own and operate the facility. Again there are even exceptions to this rule if the CPE is a hospital, DOD, police, fire, or civil defense facility where an outage cannot be tolerated.
I understand your concern for an individual?s safety, but once you compare the risk with the possibility, the needs of many outweigh the needs of an individual. A 48 VDC plant does not present much exposure to electrical shock, only some fire danger.
Consider a large 48 VDC plant of say 10,000 amps using 14-4000 ah battery strings, and 16-800 amp rectifiers. Each battery string would require a 2000 amp time-delay fuse enclosed in a disconnect device. From the battery string terminal plate you would run 2000 KCM from each polarity to the disconnect device which contains the fuse. Then from the disconnect device you would again run 2000 KCM to the power plant charge bus a short distance away. The only two places where a fault is likely to occur is on the battery terminals (which is not fused), and the charge bus. At the charge bus you have 14-4000 ah batteries and 16-800 amp rectifiers all in parallel with a fault current availability of several hundred thousand amps if the resistance allows it.
The point here is the only likely place for a fault to be incurred to allow a fuse to operate is at the battery charge bus. It is highly unlikely that even a bolted fault would operate any of the fuses in the batteries due to the resistance of the fault in series with the cable resistance at 48 VDC. From my experience and Telco experience, is the fault is vaporized which acts as the fuse to clear the fault. Yes someone can and will be hurt from the flash, but it would happen even if you had the batteries fused or not. By not fusing you eliminate an outage and protect public safety. Keep in mind these offices are a vital link to public safety including DOD, hospitals, police, fire, civil defense, FAA, long distance traffic, etc.
Sorry to be long winded, but that is the analogy used, not poor engineering.
Generally a utility is any company recognized by a city, municipality, state or local government. This is usually done by elections granting the company a monopoly. As a utility they are not required to apply for building permits nor are they ever inspected by an AHJ
As a former SWB and MCI CO power engineer of 24 years all Telco?s has debated this topic several times over the last 100 years. It really comes down to company policy. Most decide not to fuse battery strings because of the outage potential created, complexity in replacing the fuse, and the minimal risk involved.
There are two NEC code issues widely ignored by telephone companies where DC power is involved. One is fusing battery strings; the other is a de-rating conductor for adjustment factors of 310.15.B.2 contained in raceways.
SWB and MCI policy is not to use any fuses in battery strings in central offices. However there are special circumstances where they will be used such as CPE (customer premises equipment) where the facility is not owned or maintained by the Telco, or in co-located facilities where Telco does not own and operate the facility. Again there are even exceptions to this rule if the CPE is a hospital, DOD, police, fire, or civil defense facility where an outage cannot be tolerated.
I understand your concern for an individual?s safety, but once you compare the risk with the possibility, the needs of many outweigh the needs of an individual. A 48 VDC plant does not present much exposure to electrical shock, only some fire danger.
Consider a large 48 VDC plant of say 10,000 amps using 14-4000 ah battery strings, and 16-800 amp rectifiers. Each battery string would require a 2000 amp time-delay fuse enclosed in a disconnect device. From the battery string terminal plate you would run 2000 KCM from each polarity to the disconnect device which contains the fuse. Then from the disconnect device you would again run 2000 KCM to the power plant charge bus a short distance away. The only two places where a fault is likely to occur is on the battery terminals (which is not fused), and the charge bus. At the charge bus you have 14-4000 ah batteries and 16-800 amp rectifiers all in parallel with a fault current availability of several hundred thousand amps if the resistance allows it.
The point here is the only likely place for a fault to be incurred to allow a fuse to operate is at the battery charge bus. It is highly unlikely that even a bolted fault would operate any of the fuses in the batteries due to the resistance of the fault in series with the cable resistance at 48 VDC. From my experience and Telco experience, is the fault is vaporized which acts as the fuse to clear the fault. Yes someone can and will be hurt from the flash, but it would happen even if you had the batteries fused or not. By not fusing you eliminate an outage and protect public safety. Keep in mind these offices are a vital link to public safety including DOD, hospitals, police, fire, civil defense, FAA, long distance traffic, etc.
Sorry to be long winded, but that is the analogy used, not poor engineering.
Re: Batteries- fused?
Bwilson, most are referenced to ground, and bonded at the battery return bus. But it is not required. I have seen some designs float and both battery polarities fused with a ground fault detector used.
[ June 30, 2003, 02:46 PM: Message edited by: dereckbc ]
Bwilson, most are referenced to ground, and bonded at the battery return bus. But it is not required. I have seen some designs float and both battery polarities fused with a ground fault detector used.
[ June 30, 2003, 02:46 PM: Message edited by: dereckbc ]
Re: Batteries- fused?
Dereck
Looks like you and I share similar backgrounds.
I fully understand what your saying and totaly agree. I never had fused disconnects in any of my CO's. Service was of paramount importance and the DC plant was expendable.
But, I think that the wireless industry is another matter. Some AHJ's are not accepting that wireless carriers are utilities.
I'm seeing some strange installations that really concern me (e.g. A 1600 ahr VRLA battery with a connected 800a load and one 4/0 per polarity).
Dereck
Looks like you and I share similar backgrounds.
I fully understand what your saying and totaly agree. I never had fused disconnects in any of my CO's. Service was of paramount importance and the DC plant was expendable.
But, I think that the wireless industry is another matter. Some AHJ's are not accepting that wireless carriers are utilities.
I'm seeing some strange installations that really concern me (e.g. A 1600 ahr VRLA battery with a connected 800a load and one 4/0 per polarity).
Re: Batteries- fused?
You may have reason for concern. If you are talking about a single string of 1600 ah connected with 4/0 AWG, and a plant load of 800 amps you should be alarmed, not concerned. However if you are talking about 4 strings of 1600 ah batteries connected with 4/0, then no real concern unless the cable distance is long resulting in more than 1/8-volt loop drop. I assume wireless is 24 VDC and therefore 1/8-volt loop drop from batteries to charge bus at full load would be employed.
I would not consider wireless radio sites a utility, rather a service provider. On the other hand the sites are un-manned and usually remotely located. In a wireless environment I would not reference either polarity to ground, and use radio equipment that does not reference battery to the frame (pretty standard now days). I would fuse both polarities of the battery and use ground fault detection.
In addition I would specify all equipment to be isolated from incidental contact with ground by using isolation pads and bushings then SPG the equipment frames. This would prevent lightning damage, minimize ground fault outages and interference problems.
You may have reason for concern. If you are talking about a single string of 1600 ah connected with 4/0 AWG, and a plant load of 800 amps you should be alarmed, not concerned. However if you are talking about 4 strings of 1600 ah batteries connected with 4/0, then no real concern unless the cable distance is long resulting in more than 1/8-volt loop drop. I assume wireless is 24 VDC and therefore 1/8-volt loop drop from batteries to charge bus at full load would be employed.
I would not consider wireless radio sites a utility, rather a service provider. On the other hand the sites are un-manned and usually remotely located. In a wireless environment I would not reference either polarity to ground, and use radio equipment that does not reference battery to the frame (pretty standard now days). I would fuse both polarities of the battery and use ground fault detection.
In addition I would specify all equipment to be isolated from incidental contact with ground by using isolation pads and bushings then SPG the equipment frames. This would prevent lightning damage, minimize ground fault outages and interference problems.
Re: Batteries- fused?
Lbartsch, one thing I did not mention (don?t want to give away all my secrets) is rectifier battery plants are special critters and cannot be compared to AC power supply sources. As you probable know the rectifiers have current limiting circuitry and fold back the voltage when the upper limit is reached.
So if you take my example of a 10,000 amp plant using 16-800 amp rectifiers (ignore the 800-amp rating it is really 1000-amp current limiting at 100% duty cycle) and applied a dead short on the bus, the rectifiers would supply 16,000 amps continuously 24X7 without operating their internal devices. Therefore it is a mute point if the batteries are fused or not. The rectifiers are made to stay on line no matter what except power failure or lightning surge. In that case, that is what the batteries are for, why screw up a good design by adding fuses?
[ June 30, 2003, 04:31 PM: Message edited by: dereckbc ]
Lbartsch, one thing I did not mention (don?t want to give away all my secrets) is rectifier battery plants are special critters and cannot be compared to AC power supply sources. As you probable know the rectifiers have current limiting circuitry and fold back the voltage when the upper limit is reached.
So if you take my example of a 10,000 amp plant using 16-800 amp rectifiers (ignore the 800-amp rating it is really 1000-amp current limiting at 100% duty cycle) and applied a dead short on the bus, the rectifiers would supply 16,000 amps continuously 24X7 without operating their internal devices. Therefore it is a mute point if the batteries are fused or not. The rectifiers are made to stay on line no matter what except power failure or lightning surge. In that case, that is what the batteries are for, why screw up a good design by adding fuses?
[ June 30, 2003, 04:31 PM: Message edited by: dereckbc ]
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