When the sources are well known , in terms of Technical as well as Financial capabilities then the Enquiry can be limited to those certain vendors. Usually, in Public procurements,  certain limits are provided ,within which if the estimate for the purchase falls then Limited Tender Enquiry can be issued.

LTE may be adopted for higher value also , provided :

Requirement is urgent
Advertising the demand / open tendering may not be in the public interest
Sources of supply are well known and possibility of fresh source is remote
Competent authority approves

LTE copies are sent directly to the firms appearing as the Registered / approved suppliers in purchasers firm

Sufficient time (prescribed minimum or more) is to be allowed to the firms to prepare and send their offers

Late tenders (which are received after the closing time for receipt of tenders) against the OTE are not considered and opened for processing. They are ignored / rejected