Are you just supplying the engineers, in the way that an employment agency might? Or are you supplying the services / works that are being undertaken by the engineers? If you were only supplying staff, the place of supply would be in the US. But I’m assuming that you are actually supplying the services / works…
Although it’s not made clear in HMRC guidance, EU law (on which current UK law is based) includes the following within the scope of the rules for land related services:
“Article 31a(2)(l) the maintenance, renovation and repair of permanent
structures such as pipeline systems for gas, water, sewerage and the like;”
Section 2.4.13 of an explanatory note (link below) states that this would include the “maintenance, renovation or repair of telecommunication infrastructures (e.g.
the replacement of a cable network installed underground)”
https://ec.europa.eu/taxation_customs/sites/taxation/files/resources/documents/taxation/vat/how_vat_works/explanatory_notes_new_en.pdf
So if the underground networks are in the UK, that would be the place of supply, and UK VAT would be chargeable, regardless of where the customer is based.