Luton Airport Express at Bletchley this afternoon

[zwk500]

Oh i never realised what a big difference in overhead wire height there was. I am surprised the 360 can not adjust the pantograph heights but all of the other stock can. So on a 700 i presume the driver has to press something to adjust the pantograph height when going in to and coming out of the tunnels? Presumably the older 317 319 377 387 stock must have had the ability to adjust pantograph heights too?

All stock has variable height because the wire heights are lower through obstacles like bridges and tunnels and higher through things like Level Crossings. The Pantograph is usually held up by compressed air, so automatically adjusts to the wire (although this does mean there's a limit on the vertical gradients).
Presumably the issue is that the 110mph pantograph has additional elements for the higher speeds (either aerodynamic or stability) that mean when it is very low down the folding arm is not sufficiently clear of the contact wire.

 

[Haywain]

The issue, as outlined by @Pumbaa, is that the 110mph pan doesn't fit under the St Pancras Station box, which has extremely restricted clearances that the main Midland Mainline (including Platforms 1-4) don't have to worry about.

Is this something about the specific pantograph used on the 360 or about some requirements for 110mph capable pantographs in general though?

 

[zwk500]

Is this something about the specific pantograph used on the 360 or about some requirements for 110mph capable pantographs in general though?

I don't know, unfortunately, as I'm not part of the NR Gauging team. @Pumbaa may have more information, as they are the ones who shared the constraint in the first place.

 

[edwin_m]

Oh i never realised what a big difference in overhead wire height there was. I am surprised the 360 can not adjust the pantograph heights but all of the other stock can. So on a 700 i presume the driver has to press something to adjust the pantograph height when going in to and coming out of the tunnels? Presumably the older 317 319 377 387 stock must have had the ability to adjust pantograph heights too?

No, the pantograph has air pressure [Edit: not springs, at least for heavy rail] which push it up against the wire. As the wire height varies it just follows up and down.

It is quite surprising that the 360 pan won't work when the 700 does, and the photo of the 700 in #29 looks like a high speed pantograph similar to those fitted to 110mph units including the 360 in the same post. Possibly the floor of the pantograph well is a bit higher on the 360 so the same pan is below its minimum reach at St Pancras low level, or there is some adjustment to obtain 110mph compatibility which also increases the minimum reach.

 

[Haywain]

It is quite surprising that the 360 pan won't work when the 700 does, and the photo of the 700 in #29 looks like a high speed pantograph similar to those fitted to 110mph units including the 360 in the same post. Possibly the floor of the pantograph well is a bit higher on the 360 so the same pan is below its minimum reach at St Pancras low level, or there is some adjustment to obtain 110mph compatibility which also increases the minimum reach.

Looking around on the interweb, it seems that both class 700 and class 360 use the Brecknell Willis High Speed pantograph (Mk II on the 360, so likely to be similar on the later 700), so this may suggest that the limitation is something to do with the train design itself, rather than the model of pantograph in use. I wonder if your mention of pantograph well floor height is close to being the essential detail.