I’d say it’s his burden to prove to say that it’s not compliant230.28 says "adequate strength" and it is not defined. That pretty much does leave it up to how the inspector feels and 110.2.
A structural engineer could calculate it and write you a report for $500...
If the guy is reasonable, he would probably accept whatever the utility has written in their guidelines as "adequate strength" unless it is a really unusual install, which this one clearly is not.
The AHJ might have an office policy or "code interpretation" they enforce by. If that policy is written down, you have no leverage at all... but you could keep the policy handy to stay out of trouble.
If it's not written down and the guy is not reasonable about utility specs... he's wrong, but you will not win this battle.
3’ high mast
- Thread starter AC\DC
- Start date
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Our inspector says not to leave the cover off for his final inspection because sometimes the utility will go ahead and make it hot!
Master Nater
Senior Member
- Location
- Midwest
- Occupation
- Electrical Magician
slap a stupid 'guy line' back off of the mast knob, and tie it to the roof a couple of feet back. that should shut him up.
Ya I could but should?
Here we use an Arlington product that’s a rigid cast aluminum roof flange. It has a set screw that tightens against the rigid.
36” above the roof require no additional support.
I agree. Countless times I’ve seen where a 2” RMC mast has been bent from something falling on the service drop.
That messenger wire is strong enough to bend it and yet it’s still securely attached through the roof.
Arlington Industries 726-1 7-3/4 in. x 1/4 in. Aluminum Vent Pipe Flashing
Check out this, Arlington Industries 726-1 7-3/4 in. x 1/4 in. Aluminum Vent Pipe Flashing on PrairieGrit.com. The collectors marketplace!
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Ya and if a tree falls and going to bend the mast those areial cables just ripe out service no protection from preventing bent mast— and i have seen push braces puncture roof so that made a problem worse
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Did I miss it? What size is the overhead drop? I got the 50 feet length and it rises as you head to the pole.
That said 50 feet span is almost nothing and would seldom require additional bracing if only three feet of mast for typical aluminum triplex that would be used here.
That said 50 feet span is almost nothing and would seldom require additional bracing if only three feet of mast for typical aluminum triplex that would be used here.
It’s an Arlington 725-1.Is this what your talking about—-Arlington Industries 726-1 7-3/4 in. x 1/4 in. Aluminum Vent Pipe Flashing
Check out this, Arlington Industries 726-1 7-3/4 in. x 1/4 in. Aluminum Vent Pipe Flashing on PrairieGrit.com. The collectors marketplace!
Ya and if a tree falls and going to bend the mast those areial cables just ripe out service no protection from preventing bent mast— and i have seen push braces puncture roof so that made a problem worse
A bit pricey. I think I get them for around $34
- Location
- Tennessee NEC:2017
- Occupation
- Semi-Retired Electrician
We go by POCO rules here. Most allow up to 3' above roof before guying is needed. One allows up to 4'.
pipe_bender
Senior Member
- Location
- Boston
- Occupation
- Electrician
All the OP said is its a little less than 3' above the roof, but we don't know if the roof is a RMC conduit support.
A structural engineer could calculate it and write you a report for $500
Seems it should not be that hard to calculate, utility people subscribe to software that just spits that out, the OP could ask the utility to do it or
with about 5 inputs one could do a approximate Conduit Mast Deflection and Load Calculation using other inputs from the NESC:
So far we have:
1) Conduit Size: 2" RMC.
2) Span: 50 ft.
What we don't have is
3) Unbraced Length: Distance between the last acutal rigid clamp and where the ASCR is attached (lever arm).
4) Elevation Offset: (Up/downhill, e.g., 15 ft).
5) ACSR Size / type / Name: (e.g., Sparrow).
Using AI I plug in
Conduit Trade Size / Type: (2" RMC).
Span: 50'
Elevation Offset: 15'
ACSR Name: Sparrow.
Solve for Unbraced Length
It says:
===========================================================================
ENGINEERING ANALYSIS: 2" RMC SERVICE MAST STRENGTH
Scenario: 50' Span, #2 ACSR Sparrow, 15' Uphill Elevation Offset
Loading District: NESC Medium
===========================================================================
STEP 1: CONDUCTOR CONSTANTS (#2 ACSR SPARROW)
---------------------------------------------------------------------------
- Bare Weight (w_b): 0.091 lbs/ft
- Diameter (D): 0.316 inches
- Breaking Strength: 2,850 lbs
STEP 2: CALCULATE RESULTANT WEIGHT (w_r) UNDER LOAD
---------------------------------------------------------------------------
Formula: w_r = sqrt((w_wire + w_ice)^2 + (w_wind)^2) + K
- Ice (0.25" radial): Adds 0.174 lbs/ft (New Diam: 0.816")
- Wind (4 psf): (0.816/12) * 4 = 0.272 lbs/ft
- NESC Constant (K): 0.200 lbs/ft
- Resultant (w_r): sqrt((0.091+0.174)^2 + 0.272^2) + 0.20
w_r = 0.58 lbs/ft (approx)
STEP 3: CALCULATE TENSION AT MAST (T_max)
---------------------------------------------------------------------------
Because of the 15' uphill slope, the mast at the top carries more
weight than the pole at the bottom.
- Horizontal Tension (H): 500 lbs (Assumed based on 20% RBS)
- Slope Factor: In a 15' rise over 50', the mast supports
nearly the full weight of the wire span.
- Tension at Mast (P): H + (w_r * Elevation_Offset)
500 + (0.58 * 15) = 508.7 lbs (Approx 510 lbs)
STEP 4: DETERMINE CONDUIT STRENGTH LIMIT (M_a)
---------------------------------------------------------------------------
- Material: 2" Rigid Metal Conduit (RMC)
- Section Modulus (S): 0.508 in^3
- Steel Yield (sigma): 30,000 psi
- Strength Factor (SF): 0.85 (NESC Grade C / Residential)
- Allowable Moment (M_a): sigma * S * SF
30,000 * 0.508 * 0.85 = 12,954 in-lbs
STEP 5: SOLVE FOR MAX UNBRACED LENGTH (L)
---------------------------------------------------------------------------
The "Leverage" formula: M = P * L
Rearranged: L = M_a / P
L = 12,954 in-lbs / 510 lbs
L = 25.40 inches
===========================================================================
FINAL VERDICT:
Max Unbraced Length from top support to wire attachment is 25.4".
Anything higher (like 30") requires a back-guy or 2.5" RMC.
===========================================================================
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Another variable would be region, snow and ice loads would be negligible in Florida, but substantial in Minnesota.
pipe_bender
Senior Member
- Location
- Boston
- Occupation
- Electrician
With mast at bottom of hill:
===========================================================================
ENGINEERING ANALYSIS: 2" RMC SERVICE MAST STRENGTH
Scenario: 50' Span, #2 ACSR Sparrow, 15' DOWNHILL Elevation Offset
Loading District: NESC Medium
===========================================================================
STEP 1: CONDUCTOR CONSTANTS (#2 ACSR SPARROW)
---------------------------------------------------------------------------
- Bare Weight (w_b): 0.091 lbs/ft
- Diameter (D): 0.316 inches
- Breaking Strength: 2,850 lbs
STEP 2: CALCULATE RESULTANT WEIGHT (w_r) UNDER LOAD
---------------------------------------------------------------------------
- Resultant (w_r): 0.58 lbs/ft (Same as uphill scenario)
STEP 3: CALCULATE TENSION AT MAST (T_min)
---------------------------------------------------------------------------
Because the mast is at the bottom, the vertical component of the tension
actually decreases. The "Low Point" of the wire is very close to the
mast, meaning the mast is supporting very little of the wire's weight.
- Horizontal Tension (H): 500 lbs
- Slope Factor: The mast is "downhill," so it supports less
weight. Vertical load is nearly zero or even
slightly negative (uplift) in steep cases.
- Tension at Mast (P): For safety, we use the Horizontal Tension (H)
as the primary force.
P = 500 lbs
STEP 4: DETERMINE CONDUIT STRENGTH LIMIT (M_a)
---------------------------------------------------------------------------
- Material: 2" Rigid Metal Conduit (RMC)
- Allowable Moment (M_a): 12,954 in-lbs (Standard for 2" RMC)
STEP 5: SOLVE FOR MAX UNBRACED LENGTH (L)
---------------------------------------------------------------------------
The "Leverage" formula: L = M_a / P
L = 12,954 in-lbs / 500 lbs
L = 25.91 inches
===========================================================================
FINAL VERDICT:
Max Unbraced Length from top support to wire attachment is 25.9".
===========================================================================
===========================================================================
ENGINEERING ANALYSIS: 2" RMC SERVICE MAST STRENGTH
Scenario: 50' Span, #2 ACSR Sparrow, 15' DOWNHILL Elevation Offset
Loading District: NESC Medium
===========================================================================
STEP 1: CONDUCTOR CONSTANTS (#2 ACSR SPARROW)
---------------------------------------------------------------------------
- Bare Weight (w_b): 0.091 lbs/ft
- Diameter (D): 0.316 inches
- Breaking Strength: 2,850 lbs
STEP 2: CALCULATE RESULTANT WEIGHT (w_r) UNDER LOAD
---------------------------------------------------------------------------
- Resultant (w_r): 0.58 lbs/ft (Same as uphill scenario)
STEP 3: CALCULATE TENSION AT MAST (T_min)
---------------------------------------------------------------------------
Because the mast is at the bottom, the vertical component of the tension
actually decreases. The "Low Point" of the wire is very close to the
mast, meaning the mast is supporting very little of the wire's weight.
- Horizontal Tension (H): 500 lbs
- Slope Factor: The mast is "downhill," so it supports less
weight. Vertical load is nearly zero or even
slightly negative (uplift) in steep cases.
- Tension at Mast (P): For safety, we use the Horizontal Tension (H)
as the primary force.
P = 500 lbs
STEP 4: DETERMINE CONDUIT STRENGTH LIMIT (M_a)
---------------------------------------------------------------------------
- Material: 2" Rigid Metal Conduit (RMC)
- Allowable Moment (M_a): 12,954 in-lbs (Standard for 2" RMC)
STEP 5: SOLVE FOR MAX UNBRACED LENGTH (L)
---------------------------------------------------------------------------
The "Leverage" formula: L = M_a / P
L = 12,954 in-lbs / 500 lbs
L = 25.91 inches
===========================================================================
FINAL VERDICT:
Max Unbraced Length from top support to wire attachment is 25.9".
===========================================================================
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
I know some POCOs in my area require a 2 1/2" mast. We usually have to follow the POCO requirements, and they are clearly spelled out and usually exceed the NEC requirements.
Every area is different.
Every area is different.