Service Tax Credit

if service invoice in your name then you can take service tax cenvat credit. 

The erection installation contract wouldbe in your name as you have stated that vendor bills you ST. The same wouldbe available tobe set off against either your ST liability or your excise liability. You can transfer the same through the ISD route.

Assumed that you charge separately for erection installation besides value of goods supplied that suffers excise duty. As long as the subcontractors service is input service in your hands, the same qualifies for cenvat credit. The credit can be utilised for payment of excise duty or service tax.