A building has a 2000 amp 277/480 incoming service .This feeds several high voltage distibutions panels in electric closets thoughout the building then steps down for a 110/208 distribution,do these 110/208 dp panels have to stick to the six disconnect rule?or in this case 6 breakers?
distribution panels
- Thread starter m2oliva
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hurk27
Senior Member
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- Portage, Indiana NEC: 2008
Re: distribution panels
I would assume that there is some kind of main disconect on the 480/277 volt coming into this building. and since the 120/208 voltage sub system is fed off this 480/277 system the 6 disconect rule does not apply. an since they are well after the main service.
[ February 23, 2004, 07:50 PM: Message edited by: hurk27 ]
I would assume that there is some kind of main disconect on the 480/277 volt coming into this building. and since the 120/208 voltage sub system is fed off this 480/277 system the 6 disconect rule does not apply. an since they are well after the main service.
[ February 23, 2004, 07:50 PM: Message edited by: hurk27 ]
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: distribution panels
Boy that's what I get from shooting from the hip.
From what I see in 450.3(b) table, note 2. if you are using just the breakers protecting the feeders to the 120/208 panels as the protection for the transformer secondaries then it does apply. (never heard of any one doing that) but if you use a fusible disconnect for your protection of the transformers secondaries then you are covered.
[ February 23, 2004, 08:03 PM: Message edited by: hurk27 ]
Boy that's what I get from shooting from the hip.
From what I see in 450.3(b) table, note 2. if you are using just the breakers protecting the feeders to the 120/208 panels as the protection for the transformer secondaries then it does apply. (never heard of any one doing that) but if you use a fusible disconnect for your protection of the transformers secondaries then you are covered.
[ February 23, 2004, 08:03 PM: Message edited by: hurk27 ]
- Location
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- retired electrician
Re: distribution panels
If the 208/120Y panels are lighting and appliance branch circuit panels, you need a single main. See 408.16. Also 240.21(C) requires protection for the conductors between the transformer secondary and the panel. This section will also, in some cases, require a single OCPD.
Don
If the 208/120Y panels are lighting and appliance branch circuit panels, you need a single main. See 408.16. Also 240.21(C) requires protection for the conductors between the transformer secondary and the panel. This section will also, in some cases, require a single OCPD.
Don
Re: distribution panels
I know you need a single main for each panel being feed by the 110/208 distribution panel but is this panel limited to six breakers?There is no transformer secondary protection ,only the breaker in the 277/480 dp panel.The two panels and the transformer are only about five feet from each other.I belive the tranformer meets section 240-21 c2 requirements.
I know you need a single main for each panel being feed by the 110/208 distribution panel but is this panel limited to six breakers?There is no transformer secondary protection ,only the breaker in the 277/480 dp panel.The two panels and the transformer are only about five feet from each other.I belive the tranformer meets section 240-21 c2 requirements.
Re: distribution panels
M2
You have 2 problems to solve. One is the overcurrent protection of the transformer which is covered in table 450.3B and the other is protection of the secondary conductors covered in 240.21C.
Don pointed out as follows:
"If the 208/120Y panels are lighting and appliance branch circuit panels, you need a single main. See 408.16. Also 240.21(C) requires protection for the conductors between the transformer secondary and the panel. This section will also, in some cases, require a single OCPD"
240.21C2 requires that the secondary conductor
,10 ft of less, be terminated in an OC device that is equal to the capacity of the conductor.
Generally if there is only on panel the OC device may be set at 125% of the transformer secondary full load current.
Table 450.3B note 2 requires that it is permissible to install up to 6 OC devices but the sum of the 6 OC devices must not exceed the rating of a single OC device rated at 125% of the max transformer secondary current. You may install 6 panels each with a main breaker as long as you meet the rule of 125% maximum rating. The breakers in the panel can be as many as needed. The rule of 6 does not apply since the panel has a main breaker. Your post seems to indicate that you have 2 panels with main breakers. The sum of the 2 main breakers must not exceed the 125% rule.
[ February 24, 2004, 02:40 PM: Message edited by: bob ]
M2
You have 2 problems to solve. One is the overcurrent protection of the transformer which is covered in table 450.3B and the other is protection of the secondary conductors covered in 240.21C.
Don pointed out as follows:
"If the 208/120Y panels are lighting and appliance branch circuit panels, you need a single main. See 408.16. Also 240.21(C) requires protection for the conductors between the transformer secondary and the panel. This section will also, in some cases, require a single OCPD"
240.21C2 requires that the secondary conductor
,10 ft of less, be terminated in an OC device that is equal to the capacity of the conductor.
Generally if there is only on panel the OC device may be set at 125% of the transformer secondary full load current.
Table 450.3B note 2 requires that it is permissible to install up to 6 OC devices but the sum of the 6 OC devices must not exceed the rating of a single OC device rated at 125% of the max transformer secondary current. You may install 6 panels each with a main breaker as long as you meet the rule of 125% maximum rating. The breakers in the panel can be as many as needed. The rule of 6 does not apply since the panel has a main breaker. Your post seems to indicate that you have 2 panels with main breakers. The sum of the 2 main breakers must not exceed the 125% rule.
[ February 24, 2004, 02:40 PM: Message edited by: bob ]
Re: distribution panels
I believe your ok because you have a 2000 amp main breaker that shuts the whole building down.If the building had more than 6 tenants each tenant would have its own main breaker feeding there space.If there are more than 6 you need one main to shut the whole building down.
I believe your ok because you have a 2000 amp main breaker that shuts the whole building down.If the building had more than 6 tenants each tenant would have its own main breaker feeding there space.If there are more than 6 you need one main to shut the whole building down.
Re: distribution panels
If the primary overcurrent protection for the transformer does not exceed 125% of the primary FLA, or next standard size, secondary protection is not required (450.3(b)). Assuming that this is the case we are done with Article 450 as far as overcurrent protection for the transformer is concerned. There is no need to concern ourselves with secondary protection.
Now lets talk about the secondary conductors. If these conductors are ten feet or less in length and are rated not less than the device they supply (a busbar is a device), and not less than the combined computed loads on the circuits they supply, then the conductors comply with 240.21(c)(2)and are permitted to terminate on a busbar. That is providing that the busbars themselves do not require overcurrent protection.
Article 408.16(d) requires lighting and appliance branch circuit panelboards, and some power panelboards, to be protected on the secondary side of the transformer. In either case the panelboard would have ten percent or more of its circuit breakers rated 30 amps or less. If the panelboard in question does not have ten percent or more of it's breakers rated thirty amps or less individual protection is not required. There would then be no limit to the number of "disconnecting means" permitted on the secondary side of the transformer.
For example, a 500KVA 480/208-120Y transformer is supplied by two 600 Kcmil copper conductors per phase protected by an 800 amp circuit breaker. The secondary conductors of the transformer are comprised of four 350 kcmil copper conductors per phase. These conductors are ten feet in length and terminate into a 1,200 amp main lug only distribution board. This panelboard contains twelve 100 amp circuit breakers supplying a combined computed load of 950 amps. The installation complies with the code.
If the primary overcurrent protection for the transformer does not exceed 125% of the primary FLA, or next standard size, secondary protection is not required (450.3(b)). Assuming that this is the case we are done with Article 450 as far as overcurrent protection for the transformer is concerned. There is no need to concern ourselves with secondary protection.
Now lets talk about the secondary conductors. If these conductors are ten feet or less in length and are rated not less than the device they supply (a busbar is a device), and not less than the combined computed loads on the circuits they supply, then the conductors comply with 240.21(c)(2)and are permitted to terminate on a busbar. That is providing that the busbars themselves do not require overcurrent protection.
Article 408.16(d) requires lighting and appliance branch circuit panelboards, and some power panelboards, to be protected on the secondary side of the transformer. In either case the panelboard would have ten percent or more of its circuit breakers rated 30 amps or less. If the panelboard in question does not have ten percent or more of it's breakers rated thirty amps or less individual protection is not required. There would then be no limit to the number of "disconnecting means" permitted on the secondary side of the transformer.
For example, a 500KVA 480/208-120Y transformer is supplied by two 600 Kcmil copper conductors per phase protected by an 800 amp circuit breaker. The secondary conductors of the transformer are comprised of four 350 kcmil copper conductors per phase. These conductors are ten feet in length and terminate into a 1,200 amp main lug only distribution board. This panelboard contains twelve 100 amp circuit breakers supplying a combined computed load of 950 amps. The installation complies with the code.
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