240.21c

[m sleem]

Per 240.21c, do we need an ocpd between tr and secondary conductors?

 

[m sleem]

Any feedback!

 

[Dennis Alwon]

It would help to know distance and whether this is outside, inside or both. Does the MDP have a main????

 

[augie47]

In addition,, keep in mind =your "240." Code reference may not the the most applicable.
Where is the service point ? If that is a POCO transformer (or customer) you may be dealing with Art 230 rules rather than Art 240.

 

[tortuga]

In addition,, keep in mind =your "240." Code reference may not the the most applicable.
Where is the service point ? If that is a POCO transformer (or customer) you may be dealing with Art 230 rules rather than Art 240.

I agree to apply the NEC here we need to define the service point as defined in article 100.
And we need to know where the conductors are located, inside the building or outside etc.

m sleem Your in Egypt right?
Does the Ministry of Electricity recognize the NFPA 70 NEC as an acceptable standard? Have they amended it? (I would love to see a copy.) Or does you, your firm or your client just prefer to use the NEC?
And what version are you on?
I see your dealing with a three phase 50hz 13.5kV delta to 400Y230 system, such a system is not in the stock NEC yet.
With the 'minimum product standards' being deleted from the code and replaced with requiring more and more 'listed' equipment you probably will find it hard to implement the code as its intended, unless your using all North American products for some reason.

 

[m sleem]

It would help to know distance and whether this is outside, inside or both. Does the MDP have a main????

Distance = 30 m
inside building
MDP has main OCPD

 

[m sleem]

In addition,, keep in mind =your "240." Code reference may not the the most applicable.
Where is the service point ? If that is a POCO transformer (or customer) you may be dealing with Art 230 rules rather than Art 240.

It's Customer transformer not POCO

 

[m sleem]

I agree to apply the NEC here we need to define the service point as defined in article 100.
And we need to know where the conductors are located, inside the building or outside etc.

m sleem Your in Egypt right?
Does the Ministry of Electricity recognize the NFPA 70 NEC as an acceptable standard? Have they amended it? (I would love to see a copy.) Or does you, your firm or your client just prefer to use the NEC?
And what version are you on?
I see your dealing with a three phase 50hz 13.5kV delta to 400Y230 system, such a system is not in the stock NEC yet.
With the 'minimum product standards' being deleted from the code and replaced with requiring more and more 'listed' equipment you probably will find it hard to implement the code as its intended, unless your using all North American products for some reason.

Yes, i am in Egypt but i am dealing with project outside where NEC is followed.

 

[tortuga]

It's Customer transformer not POCO

Where is it metered? On the primary side?
Check out Table 450.3(A).
Whats the primary protection size and type (breaker or fuse?)
Whats the transformer rated current?
Or do you get to specify all that?

Yes, i am in Egypt but i am dealing with project outside where NEC is followed.

Cool

I haven't done many 400Y230 systems under the NEC.

 

[david luchini]

Per 240.21c, do we need an ocpd between tr and secondary conductors?

240.21(C) would require an OCPD within 7.5m secondary conductor length.

You may be able to use the 100m secondary conductor length per 240.92(C) if the installation is in a Supervised Industrial Installation.

 

[kwired]

It's Customer transformer not POCO

Where is "service point"? Customer may have to pay for the transformer even if it is on utility side of the service point, but doesn't necessarily mean they actually own it.

If this is on customer side of service point then you should have a "service disconnect" on the supply side somewhere (possibly what you identify as ACP). Then 240.21(C) applies to the conductors between the transformer and the first overcurrent device. Generally it isn't a question of whether you need overcurrent protection but rather how close does it need to be to the source and what ampacity must the conductors be, different conditions allow for variances here.

 

[tortuga]

My guess this is a situation where the power is arranged in bulk at 13.5 into a 'campus' that the POCO has limited or no access to, typically the first primary cutouts to the 'campus' are the service point. Then the feeders are run around to different buildings at 13.5.

 

[m sleem]

240.21(C) would require an OCPD within 7.5m secondary conductor length.

You may be able to use the 100m secondary conductor length per 240.92(C) if the installation is in a Supervised Industrial Installation.

240.21(C) would require an OCPD within 7.5m secondary conductor length.

Having ocpd between tr's secondary and conductors is not a common practice at least in our places, also conductors would be protected against short circuit by tr's primary ocpd, and it would be protected against overload by MDP main ocpd.

 

[kwired]

Having ocpd between tr's secondary and conductors is not a common practice at least in our places, also conductors would be protected against short circuit by tr's primary ocpd, and it would be protected against overload by MDP main ocpd.

Which is what happens with service conductors in otherwise NEC compliant applications, but you haven't made it clear exactly whether you are dealing with service conductors or secondary conductors of a separately derived system - per how NEC would apply.

Per NEC any service conductor coming into the building should have overcurrent protection at or near point of entrance, how close isn't really specified and varies from one AHJ to another. Non service conductors sort of apply similar rule but because there usually is overcurrent protection of some sort on other than service conductors rules can vary some. Still any feeder conductor/transformer secondary conductor that is not protected at or below it's ampacity is essentially subject to 240.21 (B) or (C).

 

[m sleem]

Which is what happens with service conductors in otherwise NEC compliant applications, but you haven't made it clear exactly whether you are dealing with service conductors or secondary conductors of a separately derived system - per how NEC would apply.

yes, iam dealing with service conductors.

 

[kwired]

yes, iam dealing with service conductors.

240.21 doesn't apply to service conductors.

230.70(A)(1) says: "The service disconnecting means shall be installed at a readily accessible location either outside of a building or structure or inside nearest the point of entrance of the service conductors."

230.91 says: "The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto."

So the service disconnecting means and overcurrent protection are part of the same equipment or are immediately adjacent to one another and must be near the point of entry if indoors. NEC gives no specific distance for this, there are many different ways this is interpreted by different AHJ's. Most at least want overcurrent protection within 5 or 10 feet max after entering a building with service conductors though.

 

[david luchini]

Having ocpd between tr's secondary and conductors is not a common practice at least in our places, also conductors would be protected against short circuit by tr's primary ocpd, and it would be protected against overload by MDP main ocpd.

You asked what the NEC required. What is common practice in your area is irrelevant if you are required to follow the NEC for this installation.

 

[m sleem]

You asked what the NEC required. What is common practice in your area is irrelevant if you are required to follow the NEC for this installation.

Yes, you're right, i was just trying to know the reasoning behind if the cable is already protected as i mentioned in post #13

 

[kwired]

Yes, you're right, i was just trying to know the reasoning behind if the cable is already protected as i mentioned in post #13

Per NEC services conductors are not considered to be protected. The service overcurrent protection does protect them from overload but will not protect against short circuits/ground faults that occur ahead of the service discconect. POCO may have overcurrent protection ahead of said conductors, it may very well allow much more fault current to flow before it trips than the service overcurrent protection would. Keep in mind Those service conductors are normally outside the building and don't pose as big of a threat if they overheat than if they are inside the building.

For separately derived systems - a system derived on customer side of service disconnecting means, you must provide overcurrent protection but can have "tap conductors" if they comply with provisions in 240.21.

 

[electrofelon]

Yes, you're right, i was just trying to know the reasoning behind if the cable is already protected as i mentioned in post #13

Because for certain types of faults in or after other than Delta delta transformers, the primary ocpd will not protect the secondary conductors.