airfield electrical system installation help

[RDK]

Can some of you electrical types help out a civil engineer on airport electrical work?

We are planning on redoing the underground cabling for an airfield and instead of direct bury cable and transformers we are intending to use a ducted system with transformers in pull pits. This has considerable savings for future maintenance especially in the winter.

I'm quoting from the cCanadian Electrical Code which, I am told, is more or less identical to the US code except for metric dimensions.

According to the Canadian Electrical Code Section 74, which considers airfield work unique due to the use of series type circuits, there are some specified dimension for direct bury of the ASLC (airfield series lighting cable) Rule 74-004 gives the minimum bury of 450 mm(18&quot. Can this amount be reduced by 150(6&quot mm as allowed for by rule 12-012 to 300 (12&quot mm if there is mechanical protection? Does PVC type DB-2 satisfy the protection requirements? I note that PE pipe is considered to be mechanical protection.

Rule 74-004 gives the requirement for 75 (3&quot mm lateral separation for 6.6 A cables of different series circuits. How does this apply for cables in PVC ducts? Do we need a separate duct for each cable or can we fill a duct to 40% based on cross-sectional area as allowed under 12-1014?

Rule 74-010 (2)(c) appears to allow for groups of cables installed in non-metallic cables. I cannot find any other references to the installation of ALSC in buried ducts.

Can anyone shed some light on the methods and practice for the installation of airfield cables in PVC ducted systems?


Thanks in advance Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[redtrumpet]

When obtaining CEC clarifications, the best choice is to ask the electrical inspector. I am by no means familiar with the NEC, but have seen enough of it to know that it is not the same as the CEC and you could get in trouble applying it to Canadian installations. Surely the electrical consultant for the job (please don't tell me you are doing this without an electrical consultant) can clarify the code for you? If this is the project I think it is, did you contact the engineering firm I recommended?

 

[RDK]

Greatings redtrumpet,

How's life on the Wet Coast? now -30C here. (But it's a dry cold!!)

Yep it’s the same project that we exchanged e-mail on before.

I did not contact the company that you suggested because we found an experienced engineer in one of my client’s sister companies. For the obvious reasons we are using him.

Don’t worry, I might be crazy but I’m not crazy to try something like this on my own. I just make it a practice to fully understand the major code issues on all my projects.

It is really amazing how often some professionals misunderstand basic code issues. I never trust anyone who quotes the code, especially if they quote chapter and verse. Experience has shown that they are wrong more often than not. I also never memorize the code requirements. I’ll know what they are and where to look them up but I never memorize them.

This applies to all codes. Building Electrical Plumbing …

In a speciality area like this the local inspector is out of his depth. Residential, commercial and light industrial OK but not airfield.

For example Code requires that the lower 450 mm of an aircraft hangar be rated Class 1 Division 2 and any below grade portions of the slab be class 1 division 1. I recently worked on a large renovation of a hangar. (I know I just quoted a code, I would look it up before I acted on it). I was called in part way through the project and soon discovered that the design electrical engineer had no idea that this was anything special. There are just several rules in the code that are quite specific on this issue, he had not checked, just trusted that he knew the code backwards and forward. The result was that our client had to pay to remove some work, re-do some work, not get the result promised by the designer and have the work delayed with some serious consequences to the operation.

The designer tried to blame me (it’s my fault to point out his mistakes?). Part of his defence was that the local inspector never caught his error. Luckily for me the client also had a risk consultant engineer who quickly came to my support and as a result I’m still here and the designer is not. (Not that simple as there were some other problems between the client and the design firm)
Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[redtrumpet]

Hey Rick! Going through a cold spell out here as well, -9 today (brr!) but better than the -32 Saskatoon woke up to. I fully empathize with your comment on the local inspector. I don't have the time right now to dig into this issue for you (too much billable work on the go). For clarifying the code, I advise you to purchase the CE Code Handbook. It gives both the rationale and the intent behind each rule. By knowing the rationale and intent of the rules under question, your consultant and yourself should be able to determine what depth of cover and cable separations/groupings are prudent to use for your raceway.

 

[RDK]

That is what I use instead of the actual code. A lot of book to carry but good for a civil type like myself.

Wish that there was a similar volume for the National Building Code and others.



Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[BJC]

RDK
I don't know anything about the Canadian code.
However I do know a little about underground cable and conduit.
First I would bury it the whole 18" or more. We go 36" too the top of a duct bank, the duct banks have rebar ( extra rebar at vehicle crossings ).
You can burry it locations where there is no traffic but that is an engineering fantasy. Sooner or later someone will drive an endloader, RTC or something over it. PVC in the spring thaw will be crushed. The shallower it's buried the more susceptible to damage it is. The cable in it may or may not be damaged.
Follow the standard design for duct runs wherein the centers of runs drain to manholes. All ducts get water in them. If your ducts have a swale (low point) in them you are not going to be able to pull damaged cable out and replace in cold weather.
I would consider HDPE conduit; you can plow it in, it's less likely to be damaged by vehicles. Plowing it in does not let you control duct profiles. I would install enough spare conduits to allow a cable to be quickly replaced in an emergency.
My experience with airports is that they want things designed and constructed to be easy and fast to fix/

 

[mc5w]

However, I would not bury more than 5 feet deep as too deep will keep the cables from dissipating heat.

A possible alternative to 6.6 amp circuits and incandescent bulbs is to use 120 volt medium base fixtures and install compact fluorescent refit bulbs that have the ballast built into the bulb. You can get these in sizes equivalent to 150 watt and 200 watt incandescent bulbs. Just make sure that the fixture does not block the ventilation holes in the base and that the fixture does indeed keep out moisture.

These are the least troublesome in outdoor applications because conventional compact fluorescent lampholders fail in about 2 or 3 years thanks to the matter that catalytic converters cause copper and its alloys to corrode just as fast as aluminum. I am facing having to replace 17 lampholders that are just 2 years old because Regent Lighting did not bother to clean the wires with #220 silicon carbide paper and then treat the wires with Ilsco Deox.

A second alternative to 6.6 amp circuits and incandescent bulbs is that Lights of America has been peddling a 65 watt compact fluorescent that uses a mogul Edison base and uses a seperate electronic ballast that is connected to the female lampholder. You would need to use 120 volt circuits that run off of say 600 volt primary transformers to power the external ballasts. They also peddle a 42 watt externally ballasted compact fluorescent that uses a medium Edison base. Kind of funny that a 100+ year old lampholder design is still one of the most reliable.

Small metal halide ( 50, 70, or 100 watt ) is a dark horse because I do not know of any ballasts that will give hot restrike within say5 seconds of power restoration.

Mike Cole, mc5w at earthlink dot net

 

[BJC]

RDK- heres a free book for you.

http://www.usace.army.mil/publications/armytm/tm5-811-5/

May not be specific in regards to what you doing but it's interesting and free.

mc5w
Compact fluorescents may not work up past 50 north in the praries of Kanookastan. RDK didn't say where the airport is located but it's probably not Hawaii.

 

[advidana]

Civil Engineers alway think electrical is simple.