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Inspecting the Pole
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Here's a lineman inspecting a MTO concrete truss pole and probably preparing to disconnect or remove it. Note the rusted rebar and spalled concrete on the pole because of water penetrating the concrete and expanding during the freeze/thaw cycle.
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@Rick, I believe they were checking the lights for any failed fixtures but all of these lights and poles have been taken down now.
I have a good number of pics taken around this area too showing the lights from 2009 to now...if you want I could put up a few pics of the freeway. Oh and in case you're wondering most of the old lights were AEL 125s but a few M-400R2s, M-400A3s and B2225s were mixed in.
I wonder why RIDOT uses individually switched lights on state routes over here almost all MTO installs (even intersections) are all group switched with a pole mounted relay cabinet controlled by a remote PC further up the pole.
Originally, all the state lighting and RIDOT lighting was owned, operated, and leased to them by Narragansett Electric. These lights were originally GE and Westinghouse 400W MV 240V reactor units with 120V PC receptacles. The lights were leased to RIDOT in the same way lights on wood poles are leased to towns and cities with the annual rental fee and kWh charge.
The electric company never had anything to do with relays and the same held true for RIDOT lighting. Maybe it was so they could get more money from the state becuase of more parts to service? Anyways, after NGrid took over, there have been some sections (a couple miles or so) of existing lighting that has been "retrofitted" (if that's a usable term) from individual PCs to relays over the years on I-95 and other state highways and interstates. I'm guessing they just add a relay in between the power supply and lights. I think they used multiple circuts when they wired the lights becuase there are stetches over a mile long controlled by one relay (probably with multiple poles). The lights were exactly the same specs as the ones used for wood poles, except 25ft davits or trusses were used. The were all 240V with 120V photocells.
On I-295 they replaced the poles and lights starting a few years back. Most of the lights on I-295 I have never seen lit. The lights almost seem neglected on I-295, which is essentially an alternate route for I-95 that goes around the downtown areas instead of through them. When the 250W HPS M-250R2s took over, I'm not sure if they used 240V units with 120V PCs or if they capped the second hot and used a 120V ballast. I have no clue what voltage is used for the new FCO M-400s on the tall davits though since they all use relays and shorting caps. It's msot liekly either 240V or 480V though...
The relay cabinets here look a bit like traffic light cabinets but because they are silver and have PCs sticking out of them they are easy to find.
For example a 175w MH ballast draws 1.75A on 120v and 0.45A on 480V this would mean that a 120v 15A circuit can only run 6 lumes (IIRC NEC requires a circuit with hardwired lights to be loaded at only 80% to provide a safety margin). That same 15A circuit on 480V can run an impressive 26 lumes safely.
Oh I didn't get much into voltage drop and such but higher voltage wires tend to have less voltage drop which is why power lines run a very high voltages.
In this diagram the primary line are the two wires left of the step down transformer. The step down transformers used here are centre tapped and have three wires on the secondary side. Normally the centre tap is grounded (this is why neutral is bonded (connected) to ground at the panel) and is a 0V potential. The two hot lines (L1, L2) are both at 120V potential. In this system connecting between either L1 or L2 and neutral will have a potential of 120V and connecting between L1 and L2 will have a potential of 240V.
In the case of a dryer which uses a 120/240v supply, the heating element normally requires 240v as is connected between L1 and L2, the other parts such as the motor, lights, and the timer are normally 120v and will be connected between either L1 or L2 and neutral. Ideally the 120v loads should be evenly split between L1 and L2 to avoid overloading the neutral wire.