wrong sized hole (manhole)

[GonisDowr]

We have manhole covers over the septic tank in the garden that are rusting and becoming weak.

Without lifting the cover, I measured the size of the hole (i.e. the internal part of the frame ) to be 620x470mm.

However, all the manhole covers seem to be 600x450mm or 24x18".

Is my hole non-standard or am I measuring wrongly?

Cheers.

 

[rpm]

Can you not measure the existing covers.

 

[Basher]

We have manhole covers over the septic tank in the garden that are rusting and becoming weak.

Without lifting the cover, I measured the size of the hole (i.e. the internal part of the frame ) to be 620x470mm.

However, all the manhole covers seem to be 600x450mm or 24x18".

Is my hole non-standard or am I measuring wrongly?

Cheers.

You are sort of measuring correctly, but you need to lift the cover to measure the hole size accurately.
Access cover assemblies are sold by the dimensions of the size of the inner hole, not the overall size.
I assume you would replace not only the cover, but also the frame it sits in (I imagine you won't get an exact replacement)

edit:
I've just measured my pressed steel manhole cover, and measuring like you did, it is also 620mm x 470mm.
So it looks like the right sort of 600 x 450 might fit your existing frame!
Or to put in another way - the lid of a manhole advertised as 600 x 450 is not that size!!

This claims to be your size (is it the right style of cover?)
Amazon product

 

[WC1]

Its the hole that's measured as above
This sets it out well:

How do you measure the size of a manhole cover?

No nonsense; it's the opening size you measure. But follow this article from JDP to correctly measure your manhole cover.

www.jdpipes.co.uk

 

[Plumb]

Try the metal cover one of these from wickes ones....https://www.wickes.co.uk/Clark-drain-5-Ton-Steel-Manhole-Cover+Frame---450-X-600mm/p/240730

If it fits, just use the cover, or refit the whole thing or if neither of these suits, take it back for a refund.

 

[GonisDowr]

Brilliant, thanks all. I hadn't realised that it was the, sort of, maximum size of something that can fit into the actual hole rather than the size of the cover itself.

For amateurs, it might be useful for a DIY store (not so important for a building supplies place used by pros) to state both the cover size and the hole size.