230.6 Concrete encase SE in walls

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Mikala

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Here on the Big Island of Hawaii we have a Utility, NEC (2002) and County of Hawaii requirement regarding the need to concrete encase (2 inches minimum) any conduit, carrying SE cable, that is enclosed within a wall. To date, nobody has enforced this requirement, but I?m new on the scene (as the Utility?s Customer Eng. Supv.) and I want to enforce this requirement. I?m being asked why I would want to enforce it. My answer is that the NEC 230.6, Utility Electric Service Installation Manual and County Code requires it and I believe that it is good practice to concrete encase the conduit in the wall due to safety concerns about an unprotected circuit in a dwelling.

Am I missing something here? Doesn?t everyone follow this standard in 230.6? Can anyone give me some background on why this was inserted into the NEC in the first place? I need some background information to answer a myriad of questions from people opposed to the idea.
 
Conduit encased in concrete inside a wall?? Good Lord what's next? Conduit inside of conduit and encased in 1/2" steel plate and then 6" of concrete......................? When I think a rule is "over the top" I ask one question; where is the body count? If there is sufficient evidence that a particular practice is a problem (buildings burning & people dying) then we need to address it. If we are just trying to imagine what 'COULD' happen, then leave it be and watch for problems.
 
sandsnow said:
keep service conductor length to a minimum inside a building.
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That is the phrase, isn't it Larry.

In the locations I've done service work, the maximum length of the unfused service entrance conductors inside the building has been five feet. The five feet is measured along the cable or raceway from the beginning of the structure perimeter penetration.

If I have to run the service entrance conductors more than five feet, I can do that by encasing all but five feet in concrete, or, in some other manner, install the conductors so they are "outside" the structure for all but five feet.

The distance of "five feet" is not specified in the NEC. This distance varies across the country.

Mike,

From the way you phrase your question, it sounds like you are describing concrete encasement for any and all lengths of service entrance conductors from the first point of structure perimeter penetration.
 
********The distance of "five feet" is not specified in the NEC. This distance varies across the country.*******


We are allowed 15 feet of raceway inside the building. WAC296-46B-230
 
Milala

I agree with Al. That rule probably comes from limiting the length of SE conductor inside the building. Review your standard for 230.70 and if it has a maximum length listed under 230.70(1) that is what the concrete encasement relates to.

Jim T
 
Utility transformer fusing not enough?

Utility transformer fusing not enough?

I'd been told by a retired engineer that 230.6 had been inserted for fire protection and safety of the building, so it sounds like that's the overriding reason behind it.

I'm surprised the transformer internal fuse didn't stop this, but perhaps it was an older padmount transformer without current limiting fusing? Residential transformers are all fused too with appropriately sized cutouts. Seems as if the fusing on the transformer can't be counted on for preventing this problem either, correct?

It's interesting because the latest ABB utility transformers have 2 internal fuses. One 'zero-current' fuse that will arc and extinguish at zero current, plus a current limiter fuse. Plus we (the utility) install another external fuse at each transformer.

That's the primary reason electricians, utility personnel and County inspectors are telling me that we don't need concrete encasement. Everyone feels that the fusing will blow and the line is protected by that equipment.
 
Mike

Are any of your fuses on the secondary side of the utility transformer? Most of the fusing that you described is on the high side, and is not at all designed to protect low side conductors. For example, the current limiting fuse is designed and coordinated so as to limit or prevent the likelihood of tank rupture, it has no protection value beyond that. Depending on the size of the transformer, overload protection is often not achieved at all.

In my experience, utility secondaries and services are relatively unprotected from overloads or faults.

Jim T
 
Mike

Here in So Cal the primary only fusing that the POCO uses WILL NOT stop the burn down shown in those pictures. I've seen the results first hand.

If what you guys do over there WILL stop faults like in the pictures, then I could see making a local ammendment to the Code to disregard that section. I just couldn't tell by your description if you are using any secondary conductor protection.

Someone correct me if I'm wrong. POCO's fuse to prevent nusiance blowing of fuses from short overloads. Fusing at that level will not clear a secondary conductor fault.
 
I show on my design drawings exterior service disconnects for several reasons.

1. The fire department can kill power without having to wait for the utility to drop the fuses at the pole.

2. The FD doesn't have to go inside to kill power.

3. A fault on the line between the transformer and the service disconnect is exterior to the building.

Lost one client because he insisted on six disconnects inside the building.

RC
 
Utility transformer fusing - protects the transformer!

Utility transformer fusing - protects the transformer!

You folks are absolutely correct! The fusing is there to protect the utility company's transformer (on the high side). Therefore it would allow incidents as pictured previously. I hadn't thought about the amperage possibilities at 110/208V when the fuse is located on the high side of the transformer and there 12.47kV.

So there's no real protection to the secondary conductors and I can't see any way around implementing concrete encasement whenever the SE cable is run through a wall (from overhead and underground service connections).

Thanks a whole bunch for helping clear this up for me. It's seems there's a lot more to fix over here, so I'm sure I'll be asking plenty more questions.
 
Mikala said:
So there's no real protection to the secondary conductors
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If the secondary conductors end at a single overcurrent protective device, it can be argued that the SE conductors are protected from running overloads and short circuits that are on the load side of the service disconnect OCPD.

However, the NEC permitted installation of as many as six service disconnects on one set of SE conductors and sizing the SE conductors based on the calculated load sets up the SE conductors for potentially serious overloading if the building use is altered and no qualified persons catch the overloading and force the changes indicated.

The PoCo installs it's transformer OCPD to protect the transformer, not to protect the building.

The NEC defined and approved sizing of SE conductors and grouping of disconnects, in fact, allows a curious gap in protection of the building.
 
Mike,
So there's no real protection to the secondary conductors and I can't see any way around implementing concrete encasement whenever the SE cable is run through a wall (from overhead and underground service connections).
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How far inside is are the service conductors run before the land on the service disconnect?
Don
 
Length of cable within the wall

Length of cable within the wall

If coming from overhead, it might be anywhere from 8-20 ft of conduit within the wall. If underground, it might be anywhere from 4-6 ft. within the wall.

Which brings up another question about service masts that run through a roof and down the outside wall. If the underside of the roof is enclosed (soffit?), then wouldn't the length of conduit running through that enclosed area also be required to be encased in concrete?

Also there was some discussion about SE cable run through an attic (perhaps to the other side of the house). Does this mean that cable has to be in conduit and encased in concrete?
 
Each AHJ has the authority, and often the responsibility, to limit the length of conductor allowed inside the building before it lands on an OCPD. Your organization might want to visit that standard. Our State allows 4' of conductor length before landing on a disconnect, however our local utility requires an outside disconnect for all services 400 amps and below, regardless of voltage. They allow indoor disconnects for larger ampacity services, but can't offer any rationale why.
I find those kind of decisions are as much a political football as they are a discussion of the facts. Around here, common sense doesn't always prevail.

Jim T
 
Here's another question I received from an engineer that contends that 230.6 does not require concrete encasement for service entrance conductors. His belief is that 230.3 requires service condutors supplying a building not to run through the interior of another building and that 230.6 is simply definining what it means for such conductors to be deemed outside of the building.

I personally don't agree with this thought process, but am willing to be pursuaded that I'm wrong if there's someone that knows for sure this is what it truly does refer to. Can someone help on this please?
 
Mike,

Go to the 2002 NEC Handbook. There is good explanatory text with both 230.3 and 230.6. Included in the explanatory text are two pictures, Exhibit 230.14 and Exhibit 230.15.

I agree with your engineer's take on 230.6.
230.6 Conductors Considered Outside the Building.

Conductors shall be considered outside of a building or other structure under any of the following conditions:
(1) . . .
(2) Where installed within a building or other structure in a raceway that is encased in concrete or brick not less than 50 mm (2 in.) thick
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The text doesn't read "The SE conductors inside a building shall be encased in concrete so they are considered outside the building."

No. It as much as says: "SE conductors encased in concrete are outside the building, even when the concrete is completely inside the building." Look at the brick two story wall in Exhibit 230.15. It is drawn as the back of the building, but it could easily by an interior brick wall. The SE conductors do not arrive inside that two story building until they emerge into that second story disconnect.
 
The 'light bulb' finally goes on!

The 'light bulb' finally goes on!

OK, that seems to make more sense. Let me try to re-state and then see if I finally have this correct.

1. The NEC does not require interior SE cables to be concrete encased.
2. The local utility (me) and/or local County or State codes should state the length of SE cable that is allowed to be interior.

Since the historical Utility documents require ALL interior SE cable to be concrete encased, I would need to meet with the County's Chief Electrical Inspector and agree to what is acceptable.

Note: in the past there was a letter from the County stating that 1 story homes would not require concrete encasement of SE cables. Unfortunately nobody seems to have a copy of that letter.
 
Mikala said:
OK, that seems to make more sense. Let me try to re-state and then see if I finally have this correct.

1. The NEC does not require interior SE cables to be concrete encased.
2. The local utility (me) and/or local County or State codes should state the length of SE cable that is allowed to be interior.

Since the historical Utility documents require ALL interior SE cable to be concrete encased, I would need to meet with the County's Chief Electrical Inspector and agree to what is acceptable.

...
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Re #1: Correct. However, the NEC considers service entrance conductors encased in concrete as being outside the building—230.6(2). Another consideration is that 230.70(A) requires the service disconnecting means to be installed at a readily-accessible location either outside the building or structure, or inside nearest the point of entrance of the service conductors (but not in a bathroom). From the point of entrance on, the service conductors are no longer considered outside the building. Other posters are referring to the distance between the point of entrance and the disconnecting means, where the conductors could be subject to physical damage. See 230.49 and 230.50 for protection of service entrance conductors not considered outside the building or structure.

Re #2: The NEC does not specify a maximum length for interior SE cable. Having a disconnecting means that is "nearest" the point of entrance is really quite vague. You could limit the length or go as far as to specify all SE cable is subject to physical damage and shall be protected according to 230.49 or 230.50. Note 230.49 and 230.50 are a minimum protection requirement regarding the entire length of the service entrance conductors, not just the portion inside the building.
 
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Many thanks for clearing that up!!

Many thanks for clearing that up!!

Thanks so much for the help! I feel educated enough to discuss this properly with the County now.
 
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